Updated at 2:11 p.m. ET
(CBS/AP) BOSTON - A federal appeals court Thursday declared that the Defense of Marriage Act unconstitutionally denies federal benefits to married same-sex couples, a groundbreaking ruling all but certain to wind up before the U.S. Supreme Court.
In its unanimous decision, the three-judge panel of the 1st U.S. Circuit Court of Appeals in Boston said the 1996 law that defines marriage as a union between a man and a woman deprives same-sex couples of the rights and privileges granted to heterosexual couples.
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 same-sex unions performed in states where it's legal. It also wasn't asked to address whether same-sex couples have a constitutional right to marry.
CBS News senior legal analyst Andrew Cohen said the Supreme Court could take up the case as early as its next term, which usually begins in October.
"This is a big deal," said Cohen. "It's the first federal appeals court to strike down the federal law, and it did so unanimously with two Republican appointees ruling that the statute unconstitutionally violates the equal protection rights of same-sex couples."
The law was passed at a time when it appeared Hawaii would legalize same-sex marriage. Since then, many states have instituted their own bans on same-sex 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 court judge who ruled in 2010 that the law interferes with the right of a state to define marriage and denies married same-sex couples federal benefits given to heterosexual married couples, including the ability to file joint tax returns.
"For me, it's more just about having equality and not having a system of first- and second-class marriages," said plaintiff Jonathan Knight, 32, a financial associate at Harvard Medical School who married Marlin Nabors in 2006.
"I think we can do better, as a country, than that," Knight said.
Knight said DOMA costs the couple an extra $1,000 a year because they cannot file a joint federal tax return.
Opponents of same-sex marriage blasted the decision.
"This ruling that a state can mandate to the federal government the definition of marriage for the sake of receiving federal benefits, we find really bizarre, rather arrogant, if I may say so," said Kris Mineau, president of the Massachusetts Family Institute.
Since DOMA was passed in 1996, many states have instituted their own bans on same-sex marriage, while eight states have approved it, including Massachusetts, 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.
Last year, President 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.
White House spokesman Jay Carney said the appeals court ruling is "in concert with the president's views." Mr. Obama, who once opposed same-sex marriage,.
After Mr. Obama voiced his backing of same-sex marriage, a CBS News/New York Times poll showed 38 percent of Americans said they believe same-sex couples should be allowed to get married. Twenty-four percent think they should form civil unions. Thirty-three percent are against any legal recognition at all.
Carney wouldn't say whether the government would actively seek to have DOMA overturned if the case goes before the Supreme Court.
"I can't predict what the next steps will be in handling cases of this nature," Carney said.
The ruling was met with approval from Democrats on Capitol Hill.
"When DOMA is ultimately found to be unconstitutional, once and for all, it will right a wrong of our past and we will move closer to ending a fundamental unfairness in our nation," House Minority Leader Nancy Pelosi, D-Calif., said in a statement. "We look forward to the day when we discard this discriminatory law in the dustbin of history and when all of America's families enjoy the blessings of equal protection under the law."
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 Massachusetts, Rhode Island, Maine and 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."