In a major gay rights case, the Supreme Court indicated Wednesday it could strike down the law that prevents legally married gay couples from receiving a range of federal benefits that go to other married people.

Justice Anthony Kennedy, often the decisive vote in close cases, joined the four more liberal justices in raising questions about a provision of the federal Defence of Marriage Act that is being challenged at the court.

Kennedy said the law appears to intrude on the power of states that have chosen to recognize same-sex marriages. Other justices said the law creates what Justice Ruth Bader Ginsburg called two classes of marriage, full and "skim-milk marriage."

The federal law affects a range of benefits available to married couples, including tax breaks, survivor benefits and health insurance for spouses of federal employees.

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It still is possible the court could dismiss the case for procedural reasons, though that prospect seemed less likely than it did in Tuesday’s argument over gay marriage in California.

The motivation behind the 1996 federal law, passed by large majorities in Congress and signed by President Bill Clinton, was questioned repeatedly by Justice Elena Kagan.

She read from a House of Representatives report explaining that the reason for the law was "to express moral disapproval of homosexuality." The quote produced an audible reaction in the courtroom.

Paul Clement, representing the House Republican leadership in defending the law, said the more relevant question is whether Congress had "any rational basis for the statute." He supplied one, the federal government’s interest in treating same-sex couples the same no matter where they live.

Clement said the government does not want military families "to resist transfer from West Point to Fort Sill because they’re going to lose their benefits." The U.S. Military Academy at West Point is in New York, where same-sex marriage is legal, and Fort Sill is in Oklahoma, where gay marriages are not legal.

Opposing Clement was the Obama administration’s top Supreme Court lawyer, Donald Verrilli, who said the provision of DOMA at issue, Section 3, impermissibly discriminates against gay people.

"This statute is not called the Federal Uniform Benefits Act," Verrilli said. The administration wants the court to apply a level of scrutiny it applies to discrimination against other disadvantaged groups and that makes it harder for governments to justify those laws.

Both Verrilli and Roberta Kaplan, the lawyer for the 83-year-old New Yorker who sued over DOMA, told the court that views about gay people and marriage have shifted dramatically since 1996.

"Why are you so confident in that judgment? How many states" allow same-sex unions? Justice Antonin Scalia asked Kaplan.

Nine, she said.

"So there’s been a sea change since 1996," Scalia said, doubtfully.

But Chief Justice John Roberts jumped on the idea of a rapid shift in opinion to suggest that perhaps gays and lesbians do not need special protection from the court.

"As far as I can tell, political leaders are falling all over themselves to endorse your side of the case," Roberts said.

The justices stepped into the dispute after lower federal courts ruled against the measure.

The DOMA argument followed Tuesday’s case over California’s ban on same-sex marriage, a case in which the justices indicated they might avoid a major national ruling on whether America’s gays and lesbians have a right to marry. Even without a significant ruling, the court appeared headed for a resolution that would mean the resumption of gay and lesbian weddings in California.

Marital status is relevant in more than 1,100 federal laws that include estate taxes, Social Security survivor benefits and health benefits for federal employees. Lawsuits around the country have led four federal district courts and two appeals courts to strike down the law’s Section 3, which defines marriage. In 2011, the Obama administration abandoned its defence of the law but continues to enforce it.

Legal in 9 states

Same-sex marriage is legal in nine states and the District of Columbia. The states are Connecticut, Iowa, Maine, Maryland, Massachusetts, New Hampshire, New York, Vermont and Washington. It was legal in California for less than five months in 2008.

The justices chose for their review the case of Edith Windsor, 83, of New York, who sued to challenge a $363,000 federal estate tax bill after her partner of 44 years died in 2009.

Windsor, who goes by Edie, married Thea Spyer in 2007 in Canada after doctors told them that Spyer would not live much longer. She suffered from multiple sclerosis for many years. Spyer left everything she had to Windsor.

There is no dispute that if Windsor had been married to a man, her estate tax bill would have been zero.

The U.S. 2nd Circuit Court of Appeals in New York agreed with a district judge that the provision of DOMA deprived Windsor of the constitutional guarantee of equal protection of the law.

Like the Proposition 8 case from California, Windsor’s lawsuit could falter on a legal technicality without a definitive ruling from the high court.

The House Republicans, the Obama administration and a lawyer appointed by the court especially to argue the issue spent the first 50 minutes Wednesday discussing whether the House Republican leadership can defend the law in court because the administration decided not to, and whether the administration forfeited its right to participate in the case because it changed its position and now argues that the provision is unconstitutional.

If the Supreme Court finds that it does not have the authority to hear the case, Windsor probably would still get her refund because she won in the lower courts. But there would be no definitive decision about the law from the nation’s highest court, and it would remain on the books.

Roberts and Scalia seemed most interested in this sort of outcome.

Court had doubts about Proposition 8 case

On Tuesday, the justices weighed a fundamental issue: Does the Constitution require that people be allowed to marry whom they choose, regardless of either partner’s gender? The fact that the question was in front of the Supreme Court at all was startling, given that no state recognized same-sex unions before 2003 and 40 states still don’t allow them.

But it was clear from the start of that argument in a packed courtroom that the justices, including some liberals who seemed open to gay marriage, had doubts about whether they should even be hearing the challenge to California’s Proposition 8, the state’s voter-approved gay marriage ban.

Kennedy suggested the justices could dismiss the case with no ruling at all.

Such an outcome would almost certainly allow gay marriages to resume in California but would have no impact elsewhere.

There was no majority apparent for any particular outcome, and many doubts were expressed by justices about the arguments advanced by lawyers for the opponents of gay marriage in California, by the supporters and by the Obama administration, which is in favor of same-sex marriage rights. The administration’s entry into the case followed President Barack Obama’s declaration of support for gay marriage.

Reflecting the high interest in the cases, the court was releasing an audio recording of Wednesday’s argument, just as it did Tuesday (see external links side bar above).

A somewhat smaller crowd gathered outside the court Wednesday, mainly gay marriage supporters who held American and rainbow flags. "Two, four, six, eight, we do not discriminate," a group chanted at one point. "If this isn’t the time, when is the time? When does equality come into play?" asked Laura Scott, 43, of Columbia, Md.