Qween Amar from Orlando, Fla., left, dances by Margie Phelps, right, a member of the Westboro Baptist Church, outside the Supreme Court in Washington on Tuesday. The court heard arguments on California's voter-approved ban on same-sex marriage, Proposition 8.

WASHINGTON - The Supreme Court is indicating it could strike down the law that prevents legally married gay couples from receiving a range of federal benefits that go to married people.

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

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.