Outside the Supreme Court, America’s culture wars play out.

Justice Ketanji Brown Jackson responded that leaving the question to the states was an alarming abdication of responsibility. “I’m suddenly quite worried,” she said.

The Tennessee law prohibits medical providers from prescribing puberty-delaying medication, providing hormone therapy or performing surgery to treat what the law called “purported discomfort or distress from a discordance between the minor’s sex and asserted identity.” But the law allows those same treatments for “a congenital defect, precocious puberty, disease or physical injury.”

More than 20 other states have similar laws. The court’s decision, expected by June, will almost certainly yield a major statement on transgender rights against the backdrop of a fierce public debate over the role gender identity should play in areas as varied as sports, bathrooms and pronouns.

The wide-ranging argument, which lasted two and a half hours, touched on the approaches of other nations, the relevance of a previous ruling protecting transgender workers from workplace discrimination and the rights of parents.

But the core question the justices focused on was whether the Tennessee law made distinctions based on sex, which would subject it to a demanding form of judicial scrutiny and make it harder for the law to survive.

Three families and a doctor sued to challenge the law, and the Biden administration intervened on their side. The challengers said the law violated the Constitution by denying equal protection to transgender people, primarily by discriminating against them based on sex.

J. Matthew Rice, Tennessee’s solicitor general, disagreed, arguing that the law was passed for medical purposes, and several of the conservative justices appeared to agree that it did not amount to sex discrimination.

“The burdens of the law fall equally on boys and girls, because neither can transition,” Justice Amy Coney Barrett said, repeating and seeming to endorse a point made by Justice Brett M. Kavanaugh.

Some conservative justices also seemed inclined to follow the court’s approach in overturning Roe v. Wade in 2022. In that case, the majority said regulating abortion was a matter for the states.

So, too, Justice Kavanaugh said, is gender transition care.

“The Constitution doesn’t take sides on how to resolve the medical and policy debate,” he said. “The Constitution is neutral on the question.”

Assessing the court’s ultimate direction was complicated by the silence of one justice in the conservative majority, Justice Neil M. Gorsuch, who wrote the opinion in the employment discrimination case. But it seemed probable that there were at least five votes for rejecting the equal protection challenge to the law.

Over the past decade, as the number of adolescents identifying as transgender has risen sharply, doctors around the world have weighed the risks and benefits of what is called gender-affirming care, or treatments like puberty blockers, hormones and surgeries that align their bodies with their gender identities.

Most doctors in the United States support gender treatments for adolescents, based on guidelines written by professional medical groups. But in Europe, countries including Sweden, Finland, Norway and Britain have limited gender-related medical treatments for teenagers after scientific reviews that found weak evidence of long-term benefits.

No European country has categorically banned gender medications for minors as Tennessee and more than 20 other states have done, almost entirely under Republican leadership. In Britain, for example, young people can get prescriptions for puberty blockers in clinical trials. And in contrast with states in the United States where bans extend until the age of 18, teenagers can have access to hormone treatments at the age of 16.

In Britain, restrictions on access to medical treatments for minors followed a yearslong review of the medical evidence by Dr. Hilary Cass, one of the country’s leading pediatricians. Her final report concluded that the evidence supporting the use of puberty-blocking drugs and other hormonal medications in adolescents was “remarkably weak.”

The main evidence of the care’s benefits comes from a small study from a clinic in the Netherlands in the 1990s, which found that teenagers who medically transitioned experienced long-term mental health gains. But some of the treatments bring long-term risks, such as irreversible body changes or fertility loss. And some patients who transition to a different gender later change their minds and detransition.

Advocates backing gender-affirming care have said the treatments help relieve body dysphoria. More recent studies in the United States have shown improvements in life and body satisfaction for teenagers after one or two years of treatment, though long-term data has not been published.

Several justices noted that some European countries have become wary of some kinds of transgender care.

“England’s pulling back and Sweden’s pulling back,” Justice Kavanaugh said. “It strikes me as a pretty heavy yellow light if not red light for this court to come in, the nine of us, and constitutionalize the whole area when the rest of the world, or at least the countries that have been at the forefront of this, are pumping the brakes.”

The Tennessee law is different from the European responses, said Elizabeth B. Prelogar, the U.S. solicitor general, who argued on behalf of the Biden administration. “It’s a sweeping categorical ban,” she said.

Most of the argument concerned whether the Tennessee law drew distinctions based on sex.

Justice Elena Kagan said a more straightforward approach was available. “There’s another way of looking at a law like this, maybe a more obvious way,” she said, “which is that it’s a classification based on transgender status.”

Among the factors the court has used to determine whether to grant protected status to groups warranting heightened scrutiny are whether their traits are immutable and whether they have political power.

Justice Samuel A. Alito Jr. said gender identity is not always fixed and so cannot be said to be immutable.

“There are individuals who are born male, assigned male at birth, who at one point identify as female, but then later come to identify as male,” he said.

Chase B. Strangio, a lawyer with the American Civil Liberties Union representing the families challenging the law, said that “the discordance between a person’s birth sex and gender identity has a strong biological basis and would satisfy an immutability test.”

Justice Kavanaugh asked questions about sports, suggesting that it may not be “logically and legally possible” to strike down the Tennessee law but to uphold “laws that limit women’s and girls sports to exclude transgender athletes.”

Ms. Prelogar responded that the two kinds of laws are different. Letting transgender women play on sports teams affects the other players, she said.

“There’s nothing like this here,” she added. “Allowing transgender individuals who have carefully thought about this and consulted with their parents and their medical team to access these medications that have health benefits recognized here and abroad in no way affects the rights of other people.”

The Supreme Court has only once before heard arguments in a case on transgender rights. The question in that case, Bostock v. Clayton County, decided in 2020, was whether a federal civil rights law protected transgender people from employment discrimination.

The court said yes, relying on the law’s prohibition of discrimination “because of sex.”

“It is impossible,” Justice Gorsuch wrote for a six-justice majority, “to discriminate against a person for being homosexual or transgender without discriminating against that individual based on sex.”

The Bostock case turned on the language of a federal law, while the new case concerns the equal protection clause of the 14th Amendment. Last year, a divided three-judge panel of the U.S. Court of Appeals for the Sixth Circuit, in Cincinnati, ruled that Tennessee’s law had a rational basis as a reasonable legislative response to contested medical evidence.

Judge Jeffrey S. Sutton, writing for the majority, said the law did not draw distinctions based on sex.

“The laws regulate sex-transition treatments for all minors, regardless of sex,” he wrote, adding: “No minor may receive puberty blockers or hormones or surgery in order to transition from one sex to another. Such an across-the-board regulation lacks any of the hallmarks of sex discrimination.”

That meant, Judge Sutton wrote, that the law was subject to only a relaxed and deferential form of judicial scrutiny called rational basis review.

“The unsettled, developing, in truth still experimental, nature of treatments in this area surely permits more than one policy approach,” Judge Sutton wrote, “and the Constitution does not favor one over the other.”

The families and the Biden administration filed separate petitions seeking Supreme Court review. The families’ petition posed two questions: whether the law violated the equal protection clause and whether it ran afoul of “the fundamental right of parents to make decisions concerning the medical care of their children.” The administration pressed only the equal protection claim.

The court granted only the administration’s petition, meaning that the question of parental rights is not directly before the justices.

Justice Kavanaugh asked about it anyway.

“Why not trust parents rather than the state,” he said, “particularly in a situation, as General Prelogar said, where there’s not the kind of direct harm to third parties that you might see in other contexts, like sports?”

Mr. Rice, representing Tennessee, said “the parental rights question is not before this court” and added that there are times when “the states, in their traditional role as regulators, have had to intervene” to protect children.

It is the second major case heard by the court on transgender rights, and the outcome could have sweeping ramifications for more than 20 other states that have similar laws.

Even before arguments got underway, the undercurrents of America’s culture wars pulsed through the crowd. Speakers from both sides blasted their speeches over microphones, each trying to drown out the other. Senator Ed Markey, Democrat of Massachusetts, was nearly shouting when he said it was a “moral obligation” to defend the rights of transgender people.

From across a thin line of fencing, supporters of transgender rights derided their counterparts as “fascists” and danced to upbeat music between speeches that depicted the Tennessee law as discriminatory and hateful. One supporter held aloft a towering pole with two supersized flags — American and pride — under it, while many others carried transgender flags, the five-strip banner with light blue, pink and white.

Outnumbered, the supporters of the Tennessee law more often expressed their perspective through posters than chants. Standing before a sign reading “Stop the Harm,” they framed the measure as an effort to protect children from “barbaric doctors.”

Annie Eliason, the mother of a 19-year-old transgender daughter who started hormone therapy at 14, said she was there to save the access to care that her daughter “desperately needed.” Her daughter plunged into depression when her gender dysphoria became evident in her early teens and recovered only after receiving the treatment, Ms. Eliason said.

“It’s magical when children are allowed to be themselves,” she said. “They thrive. They can live beautiful, amazing lives.”

But Claire Abernathy, who had received hormonal therapy since she was 9 but later discontinued the treatment, said she supported Tennessee banning such care because of the health complications she experienced afterward.

“I wish that they had said no to me,” Ms. Abernathy said, referring to her parents and state government, even though minors already need parental consent for any form of gender-affirming care.

Inside the court, during arguments that stretched two-and-a-half hours, the justices presided with obvious interest, holding eye contact while speaking with lawyers for each side and donning reading glasses to review papers before them. Justice Neil M. Gorsuch did not speak or ask questions despite subtle attempts by his colleagues to pull him into the discussion, leaning forward and nodding instead.

The most animated justice was Samuel A. Alito Jr., part of the conservative’s majority, who rocked in his chair while listening and often fixed a gaze when he seemed to disagree with the government’s lawyers, Elizabeth B. Prelogar, the solicitor general, and Chase B. Strangio, the lawyer for the American Civil Liberties Union, who is transgender.

Back outside the court, Jace Woodrum, an executive director at the A.C.L.U. who transitioned in his early 30s, said preserving access to transition therapy would protect transgender adolescents, who have high rates of depression, suicidal thoughts and self-harm. Some evidence suggests that puberty blockers and hormones, in the short-term, could improve their mental health.

Mr. Woodrum said the country should not create law based on the experiences of a few people who did not benefit from the care.

“This is, and should be, an issue that rises above partisanship,” Mr. Woodrum said. “In fact, this Tennessee law was initially blocked by a Trump appointed district court judge in Tennessee.”

And Chase Strangio, the first openly transgender lawyer to argue a case before the Supreme Court, seemed to nod to the uncertainty of the outcome for his clients and other transgender youth: “Whatever happens today, tomorrow, and in the months and years to come, I trust that we will come together to fight for the realized promise of our Constitution’s guarantee of equal protection for all.”

“If we win the case and the court decides to allow state legislatures to make these decisions, it means the ordinary course of democracy proceeds and people will continue to debate these issues,” Mr. Skrmetti said. “If we lose this case and the courts subvert the ability of the people’s elected representatives to make these decisions, then I think you’ll see a substantial amount of frustration because people will feel alienated from the political process.”

A decision in the case, experts say, also could affect any national legislation that may emerge from the new Republican-controlled Congress.

“The Supreme Court could say, ‘This only applies to health care for minors,’ but why?” said Jessica Clarke, a law professor at the University of Southern California who co-wrote a brief in support of the Biden administration’s side of the case, challenging a Tennessee ban on transition treatments for minors.

Jim Campbell, chief counsel for Alliance Defending Freedom, a conservative legal group that filed a brief in support of Tennessee, said he expected that the court’s opinion in Skrmetti would dictate the outcome of challenges to state policies that deny coverage for gender transition procedures for Medicaid recipients or employees on state health insurance plans.

“How it affects the bathroom issues, sports issues — I don’t think it’s like a one-for-one that necessarily what the court does here, it’s going to do in those cases,” Mr. Campbell said, “but I do think it’s going to significantly influence them.”

The central dispute in the case revolves around whether a Tennessee law banning several forms of medical care for transgender youth makes distinctions on the basis of sex. If the Supreme Court finds that it does, then laws in over a dozen states that prohibit transgender students from using bathrooms and participating on sports teams that align with their gender identity might not withstand constitutional challenges — or would at least require a higher level of justification to do so.

In its court briefings, Tennessee argues that the law does not make such distinctions because the ban on transition treatment is applied to both boys and girls. The plaintiffs say that it does because the ban is selective by sex: It allows minors to use these medical treatments, but only if they’re not using them for gender transition. For example, they said, testosterone may be prescribed for teens identified as male at birth, but not for those identified as female.

Tennessee’s response, if accepted by the justices, could have far-reaching effect, legal scholars said. The state argues that biological justifications for the bans are not the kind of sex stereotypes the court struck down in its 1996 landmark decision in the case United States v. Virginia. In that case, the Supreme Court found that Virginia’s reason for excluding women from the Virginia Military Institute, which only male students could attend at the time, was an unconstitutional sex stereotype.

But that is not the same, Tennessee argues, as drawing a distinction between the hormone therapies available to adolescent girls and boys, who typically have different levels of testosterone and estrogen. The state cites Justice Samuel A. Alito Jr.’s observation in the Dobbs v. Jackson Women’s Health Organization opinion that regulating abortion is not a form of sex discrimination because only women can get abortions.

“Saying that a woman shouldn’t hold a specific job because she’s ill-fitted to do it, that’s a stereotype,” said Mr. Campbell. “Saying that a woman produces a higher level of estrogen than a man does is not a stereotype. That’s just a biological difference.”

But according to Courtney Cahill, a constitutional law professor at the University of California, Irvine, the Supreme Court’s ruling in the Virginia Military Institute case actually supports the plaintiffs’ position in the Tennessee case, because the state’s argument for excluding women from admission was also rooted in biological differences between the sexes.

“I can see it leading to a big step back for women and L.G.B.T.Q. people,” Ms. Cahill said, “if biology is allowed to act as a constraint on sex discrimination.”

Still, James Blumstein, a law professor at Vanderbilt University who submitted a brief on behalf of Tennessee, said he thought a ruling for the state could be construed far more narrowly. The state, he said, has an interest in protecting the health of minors, including from their parents and doctors. But in his mind, a ruling in the case on those grounds would have no bearing on sports, bathrooms or adults.

“It seems quite wide of the mark to attempt to fit these categorizations into a sex-based discrimination context,” he wrote.

That would ordinarily mean that there would be nothing left for the justices to decide, as both sides would then agree that the law was constitutional.

Something similar happened in 2017, the last time President-elect Donald J. Trump took office. That March, after the Trump administration reversed positions on the rights of transgender students, the Supreme Court dismissed a case it had previously agreed to decide, on whether a transgender boy in Virginia could use the boys’ bathroom at his high school.

But there is a wrinkle here. The challenge to the Tennessee law was initially brought by three families and a doctor, with the Biden administration intervening on their side. The families and the government filed separate petitions seeking review in the Supreme Court, and the justices accepted only the one from the government.

Rather than dismissing the case, the court could belatedly grant the companion petition. The court could hear another argument, or it could rely on the one on Wednesday, when a lawyer for the families, Chase Strangio of the American Civil Liberties Union, will argue alongside Elizabeth B. Prelogar, the U.S. solicitor general, representing the Biden administration.

New administrations used to change positions sparingly. The Obama administration, for instance, did not flip positions in any cases on assuming office. The first Trump administration was considerably bolder. It changed positions in four major cases in its first full Supreme Court term, including ones on workers’ rights and voting rolls, prevailing in all four.

The Biden administration was not shy about switching positions, either. It disavowed the approaches of the Trump administration five times and lost four of those cases, according to a tally by Thomas Wolf of the Brennan Center for Justice.

At the same time, it would be a mistake to read too much into his silence or his 2020 majority opinion, which was tightly bound to the text of the law, Title VII of the Civil Rights Act of 1964. Justice Gorsuch is a committed textualist, meaning that he interprets the plain words of statutes without regard to their apparent purpose.

Even so, he said he found the task difficult when the case was argued in 2019.

“We’re talking about the text,” he said. “It’s close. The judge finds it very close. At the end of the day, should he or she take into consideration the massive social upheaval that would be entailed in such a decision?”

When he issued his majority opinion eight months later, he wrote that the meaning of the statute was plain in forbidding employers from firing workers based on their gender identity. Justice Gorsuch focused on the statutory phrase “because of sex.”

But he stressed that the ruling was in other ways limited. “We do not purport to address bathrooms, locker rooms or anything else of the kind,” he wrote. “Whether other policies and practices might or might not qualify as unlawful discrimination or find justifications under other provisions of Title VII are questions for future cases, not these.”

The case now before the justices does not turn on the Civil Rights Act but on the Constitution’s equal protection clause.

Last year, in his concurring opinion in the court’s decision striking down the race-conscious admissions programs at Harvard and the University of North Carolina, Justice Gorsuch reflected on the “obvious differences” between the Civil Rights Act and the Constitution.

“That such differently worded provisions should mean the same thing is implausible on its face,” he wrote.

The court heard arguments in its only other case on transgender rights, Bostock v. Clayton County, on Oct. 8, 2019. The decision arrived on June 15, 2020.

Scholars have given varied explanations for why the biggest cases tend to land in June, no matter when they were argued. One is that justices keep polishing the opinions that will define their legacies until the last possible moment.

A 2015 study in the Duke Law Journal suggested a more personal reason: “The justices, most of whom have busy social schedules in Washington, may want to avoid tensions at their social functions by clustering the most controversial cases in the last week or two of the term — that is, just before they leave Washington for their summer recess.”

Demand for puberty-blocking medication and hormone therapy among transgender youth has not been studied extensively, but only a small fraction of minors who identify as transgender currently receive gender-transition treatments. The institute researchers wrote that thousands of young people living in states where bans have been enacted “have received these treatments in the past, are receiving them currently, or may need to receive them in the future.’’

The Supreme Court case revolves around a ban on gender-transition treatments for minors in Tennessee, which is home to about 3,100 transgender teenagers, the researchers say. Nationally, about 1.4 percent of Americans between 13 and 17 identify as transgender, according to a 2022 report by the Williams Institute, which applied statistical modeling to data from several government sources.

A recent study by the Centers for Disease Control and Prevention, based on a 2023 survey of teenagers in 20,000 high schools across the United States, found that 3.3 percent of high school students identified as transgender with an additional 2.2 percent of students saying that they were unsure if they were transgender.

One review of health insurance claims by Reuters found that about 122,000 patients between 6 and 17 in the United States were diagnosed with gender dysphoria — a condition marked by a distressing sense of disconnection between a person’s physical appearance and gender identity — from 2017 to 2021. In the same period, about 5,000 in the group began puberty-blocking medication, and 15,000 began hormone therapy.

About 190,000 young people who identify as transgender live in the rest of the states where access to puberty-blocking medication and hormone therapy is protected by law, or is neither protected nor prohibited.

Matthew Rice, Tennessee's lawyer, says that Kagan is suggesting that the law has an improper purpose. But actually, he says, what the state cares about is preventing regret and detransitioning, by making sure minors have time to appreciate their sex before making a life-altering change.

He compares the two examples to using morphine to manage pain versus using it to assist in suicide. The effects on the body are different, he says, allowing it to be regulated differently.

He then worked at Williams & Connolly, a prestigious law firm based in Washington, D.C. A native of Johnson City, Tenn., Mr. Rice returned to his home state to work in the state attorney general’s office in 2022.

He started work there shortly before Attorney General Jonathan Skrmetti was appointed to an eight-year term. Under Mr. Skrmetti, the office has defended Tennessee’s efforts to limit access to gender-affirming care and public drag shows and has successfully challenged the Biden administration’s efforts to expand Title IX protections to L.G.B.T.Q. students.

As solicitor general, Mr. Rice and his office are tasked with all litigation before a higher court, ranging from the Tennessee Court of Appeals to the Supreme Court.

Mr. Rice, who was named to his position in March, is expected to argue that limiting access to gender-affirming care is not discriminatory because the state is obligated to protect children. In legal documents, Tennessee lawyers have argued there is a distinction between using hormones and puberty blockers to help transgender children transition, and using the same sorts of medications to treat young people for other issues.

“Tennessee, like many other states, acted to ensure that minors do not receive these treatments until they can fully understand the lifelong consequences or until the science is developed to the point that Tennessee might take a different view of their efficacy,” the state wrote in one brief to the court.

Strangio explains it like this: A "birth-sex male" who hits puberty too early can receive puberty blockers in order to later develop like other boys. A "birth-sex female" may also want to to receive puberty blockers in order to undergo puberty as a typical boy. So it is the same purpose, Strangio says, and what makes the treatment prohibited for the latter person is sex.

Evidence shows that transgender people are at higher risk of thinking about suicide and attempting it, as well as actual suicides. Whether medical treatment for minors reduces that risk is contested. You can read more about the research on the topic here and here.

Asked at a news conference yesterday about the plaintiffs’ chances given the conservative makeup of the Supreme Court, Strangio acknowledged that it might be an uphill battle, referencing the 1986 case in which the court held that there was no constitutional protection for sodomy. “It was a bleak moment.” But he noted that 17 years later, the justices found the Texas statute criminalizing sodomy unconstitutional.

Last year, when the court ruled that a transgender girl could compete on the girls’ cross country and track teams at her middle school in West Virginia while her appeal moved forward, Justice Thomas joined a dissent by Justice Alito indicating that states are entitled to enact laws “restricting participation in women’s or girls’ sports based on genes or physiological or anatomical characteristics.”

The court’s brief order, which let stand an appeals court’s temporary injunction, gave no reasons, which is not unusual when the justices rule on emergency applications filed on what critics call the court’s shadow docket.

In 2020, when the Supreme Court turned down an emergency request from Idaho prison officials to block court-ordered sex reassignment surgery for a transgender prisoner, Justices Thomas and Alito said they would have granted the request but did not say why.

On one occasion, though, Justice Thomas did file an extended dissent in a case involving gender identity.

Last December, the court announced that it would not hear a First Amendment challenge to a Washington State law banning professional counseling services intended to change a minor’s gender identity or sexual orientation.

The law forbids licensed therapists there from performing conversion therapy, which it defined to include “efforts to change behaviors or gender expressions, or to eliminate or reduce sexual or romantic attractions or feelings toward individuals of the same sex.” The law permits counseling that promotes “acceptance, support and understanding.”

Justice Thomas wrote that the court should have agreed to hear the case.

“This petition asks us to consider whether Washington can censor counselors who help minors accept their biological sex,” he wrote. “Because this question has divided the courts of appeals and strikes at the heart of the First Amendment, I would grant review.”

Justice Thomas said the state had violated the Constitution by choosing sides in the “fierce public debate over how best to help minors with gender dysphoria,” the psychological distress caused by incongruence between experienced gender and that assigned at birth.

“As all parents know, when your child is suffering, you are suffering,” Mr. Strangio, the father of a 12-year-old, said in a news conference earlier this week. “My heart especially aches for the parents who spent years watching their children in distress and eventually found relief in the medical care that Tennessee now overrides their judgment to ban.”

Supporters of the Tennessee law and similar restrictions in other states argue that doctors mislead parents into thinking that gender transition treatment is necessary for their children without informing them of potential risks.

The arguments in the case come as national political figures, including some Democrats, have pushed back on transgender athletes participating in sports. Republicans in Congress have also moved to bar transgender people from using bathrooms on Capitol Hill that align with their gender identity.

In the case, Mr. Strangio represents two transgender boys, a transgender girl, their parents and a Tennessee doctor who provided gender-transition treatments to minors before such treatment became illegal. The minors say the treatments have improved their happiness and sense of well-being. The Justice Department also intervened in the suit to challenge the law.

The other conservative justice who joined Gorsuch on that majority opinion was Chief Justice Roberts. Justices Alito, Thomas and Kavanaugh dissented.