WASHINGTON — 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 Defense 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.

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.