The Obama administration urged the Supreme Court on Friday to throw out a section of a 1996 federal law that prohibits recognition of same-sex marriage.

The brief was filed Friday in United States v. Windsor, a case challenging Section 3 of the Defense of Marriage Act, or DOMA, the law that legally declares marriage to be only between a man and a woman. That section allows state and federal authorities to deny benefits to same-sex couples that are commonplace for heterosexual couples, like insurance for government workers and Social Security survivors' benefits.

Oral arguments are scheduled for March 27.

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In its brief (.pdf), the U.S. bluntly declares: "Section 3 of DOMA violates the fundamental constitutional guarantee of equal protection. 

"The law denies to tens of thousands of same-sex couples who are legally married under state law an array of important federal benefits that are available to legally married opposite-sex couples," said the brief, which was signed by Solicitor General Donald Verrilli, the government's chief trial lawyer. "Because this discrimination cannot be justified as substantially furthering any important governmental interest, Section 3 is unconstitutional."

In a footnote, the brief mentions California's Proposition 8 and similar measures in other states as evidence that anti-gay discrimination remains a major problem.

In effect, the U.S. is asking the court to change DOMA to set a higher bar for courts to approve laws that discriminate against gay men and lesbians, Lyle Denniston, a Supreme Court expert, wrote on the influential ScotusBlog.

President Barack Obama announced in 2011 that the U.S. would no longer enforce DOMA, but "this is the first time the federal government has proposed that constitutional test in a gay rights case before the Supreme Court," Denniston writes. "The court itself has never specified just what constitutional standard it will apply in such cases, but it may have to settle that this term."

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Updated at 2:30 p.m. ET: A federal appeals court has ruled that the Defense of Marriage Act, a law that denies a host of federal benefits to same-sex married couples, is unconstitutional.

The 1st U.S. Circuit Court of Appeals in Boston ruled Thursday that the act known as DoMA, which defines marriage as a union between a man and a woman, discriminates against gay couples.

The law was passed in 1996 at a time when it appeared Hawaii would legalize gay marriage. Since then, many states have instituted their own bans on gay marriage, while eight states have approved it, led by Massachusetts in 2004, and followed by Connecticut, New York, Iowa, New Hampshire, Vermont, Maryland, Washington state and the District of Columbia. Maryland and Washington’s laws are not yet in effect and may be subject to referendums.

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The appeals court agreed with a lower court judge who ruled in 2010 that the law is unconstitutional because it interferes with the right of a state to define marriage and denies married gay couples federal benefits given to heterosexual married couples, including the ability to file joint tax returns.

The 1st Circuit said its ruling wouldn’t be enforced until the U.S. Supreme Court decides the case, meaning that same-sex married couples will not be eligible to receive the economic benefits denied by DOMA until the high court rules.

Attorney Paul Clement, who represented the House of Representatives in defending DOMA, told msnbc.com that no decisions on legal strategy have been made.

“But we have always been clear we expect this matter ultimately to be decided by the Supreme Court, and that has not changed,” he said.

Gay & Lesbian Advocates & Defenders, the Boston-based legal group that brought one of the lawsuits on behalf of gay married couples, said the court agreed with the couples that it is unconstitutional because it takes one group of legally married people and treats them as "a different class" by making them ineligible for benefits given to other married couples.

"We’ve been working on this issue for so many years, and for the court to acknowledge that yes, same-sex couples are legally married, just as any other couple, is fantastic and extraordinary," said Lee Swislow, GLAD’s executive director.

Earlier: Illinois same-sex couples sue for right to marry

During arguments before the court last month, a lawyer for gay married couples said the law amounts to "across-the-board disrespect." The couples argued that the power to define and regulate marriage had been left to the states for more than 200 years before Congress passed DoMA.

An attorney defending the law argued that Congress had a rational basis for passing it in 1996, when opponents worried that states would be forced to recognize gay marriages performed elsewhere. The group said Congress wanted to preserve a traditional and uniform definition of marriage and has the power to define terms used to federal statutes to distribute federal benefits.

More than 1,000 benefits in question
Two California federal judges earlier said the act violated constitutional standards.

Judge Claudia Wilken of Oakland ruled May 24 that the law legalized bigotry by withholding more than 1,000 federal benefits -- such as joint tax filing, Social Security survivor payments and immigration sponsorship -- from gays and lesbians legally married under state law.

Judge Jeffrey White of San Francisco also declared DoMA unconstitutional and ordered the government to provide family insurance coverage to the wife of a lesbian court employee. White's ruling has been appealed to the Ninth U.S. Circuit Court of Appeals, which will hear the case in September.

President Barack Obama withdrew his administration's defense of the law in February 2011, saying he considered it unconstitutional. House Speaker John Boehner convened the Bipartisan Legal Advisory Group to defend it. The legal group argued the case before the appeals court.

On May 9, Obama declared in an interview with ABC News his unequivocal support for gay marriage, becoming the first president to endorse the idea.

Obama said, "I have hesitated on gay marriage in part because I thought that civil unions would be sufficient." He added that he "was sensitive to the fact that for a lot of people the word 'marriage' was something that invokes very powerful traditions, religious beliefs and so forth."

Now, he said, "it is important for me personally to go ahead and affirm that same-sex couples should be able to get married."

Two of the three judges who decided the case Thursday were Republican appointees, while the other was a Democratic appointee. Judge Michael Boudin, who wrote the decision, was appointed by President George H.W. Bush, while Judge Juan Torruella was appointed by President Ronald Reagan. Chief Judge Sandra Lynch is an appointee of President Bill Clinton.

Groups slam, praise ruling

• “Liberal federal judges in Massachusetts and California have resorted to making up legal standards in order to justify redefining marriage,” said Brian Brown, president of The National Organization for Marriage. “They realize the legal precedent doesn’t allow them to redefine marriage, so they are making up new standards to justify imposing their values on the rest of the nation. It is clear that the U.S. Supreme Court is going to have to resolve this issue once and for all. … It’s obvious that the federal courts on both coasts are intent on imposing their liberal, elitist views of marriage on the American people.”
• "We are thrilled that another court -- this time, the 1st Circuit Court of Appeals -- has ruled that it is unconstitutional to deny respect to the marriages of lesbian and gay couples," said Camilla Taylor, National Marriage Project Director for Lambda Legal. “We congratulate our colleagues at GLAD for achieving this wonderful victory."
• "This is one more powerful statement now from an appellate court following four other federal courts that the so-called Defense of Marriage Act is indefensible under the constitution and should be discarded," Evan Wolfson, founder and president of Freedom to Marry, told msnbc.com. "It’s obviously a great victory not just for families harmed by federal marriage discrimination but for the country. Hopefully it will help us get back to our normal practice of the federal government respecting the marriages celebrated in the states without a gay exception."

Msnbc.com's Miranda Leitsinger and Jim Gold and The Associated Press contributed to this report.

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