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A federal appeals court ruled Thursday against a central provision of the Defense of Marriage Act, a groundbreaking decision that tees up a potential battle before the Supreme Court.

The three-judge panel of the 1st U.S. Circuit Court of Appeals in Boston ruled that the provision defining marriage as between a man and woman is unconstitutional in that it denies gay couples the rights granted to heterosexual couples.

The unanimous decision once again brings the issue of gay marriage to the fore of the nation's political debate. It comes just a few weeks after President Obama announced his support for gay marriage -- in the wake of that announcement, some gay advocacy groups have stepped up pressure on Washington to fight DOMA.

Considering the potential Supreme Court battle ahead, White House Press Secretary Jay Carney was asked Thursday whether the Obama administration would actively fight for overturning the law, which was originally signed by Democratic President Bill Clinton.

Carney noted that the Obama administration has concluded the section in question is unconstitutional and will no longer defend it in court. Without commenting on what steps the administration might take in the future, he described the Justice Department as an "active participant" in the case.

"There's no question that this is in concert with the president's views," he said. "I can't predict what the next steps will be in handling cases of this nature."

Gay marriage advocates hailed Thursday's decision, while its opponents condemned it.

"Society should protect and strengthen marriage, not undermine it. The federal Defense of Marriage Act provides that type of protection, and we trust the U.S. Supreme Court will reverse the 1st Circuit's erroneous decision," said a statement from Alliance Defense Fund Legal Counsel Dale Schowengerdt.

The court didn't rule on the law's more politically combustible provision, which said states without same-sex marriage cannot be forced to recognize gay unions performed in states where it's legal. It also wasn't asked to address whether gay couples have a constitutional right to marry.

The law was passed 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.

The court, the first federal appeals panel to deem the benefits section of the law unconstitutional, agreed with a lower level judge who ruled in 2010 that the law 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.

That's because the ruling only applies to states within the circuit, including Massachusetts, Rhode Island, Maine, New Hampshire and Puerto Rico. Only the Supreme Court has the final say in deciding whether a law passed by Congress is unconstitutional.

Although most Americans live in states where the law still is that marriage can only be the union of a man and a woman, the power to define marriage had always been left to the individual states before Congress passed DOMA, the appeals court said in its ruling.

"One virtue of federalism is that it permits this diversity of governance based on local choice, but this applies as well to the states that have chosen to legalize same-sex marriage," Judge Michael Boudin wrote for the court. "Under current Supreme Court authority, Congress' denial of federal benefits to same-sex couples lawfully married in Massachusetts has not been adequately supported by any permissible federal interest."

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.

Since DOMA was passed in 1996, many states have instituted their own bans on gay marriage. The eight states that have approved gay marriage are Massachusetts, Connecticut, New York, Iowa, New Hampshire, Vermont, Maryland and Washington state. The District of Columbia has also has approved it. Maryland and Washington's laws are not yet in effect and may be subject to referendums.

Last year, Obama announced the U.S. Department of Justice would no longer defend the constitutionality of the law. After that, House Speaker John Boehner convened the Bipartisan Legal Advisory Group to defend it. The legal group argued the case before the appeals court.
Gay & Lesbian Advocates & Defenders, the Boston-based legal group that brought one of the lawsuits on behalf of gay married couples, said the law 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.

Two of the three judges who decided the case Thursday were Republican appointees, while the other was a Democratic appointee. Boudin 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.

The Associated Press contributed to this report.