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 defense of the law but continues to enforce it.