A federal appeals court Tuesday refused to revisit its February ruling striking down California's ban on gay marriage, marking another in a series of legal victories for gay rights proponents and setting up a possible U.S. Supreme Court showdown.

A three-judge panel of the 9th U.S. Circuit Court of Appeals in San Francisco ruled in February that California voters abused their initiative power in 2008 in approving Proposition 8, which put a halt to a brief period in California when same-sex couples could legally wed. In a 2-1 decision, the panel said voters used their "initiative power to target a minority group and withdraw a right that it possessed," violating the U.S. Constitution's guarantee of equal protection.

That ruling stood Tuesday when supporters of Proposition 8 failed to win support for a rehearing by a majority of the 9th Circuit's 25 active judges. A court-ordered stay on same-sex marriages will remain in place during the appeals process.

As gay marriage supporters exulted over Tuesday's decision, Proposition 8 backers announced they would file an appeal to the U.S. Supreme Court in hopes of reaffirming California's gay marriage ban.

"I think now this will get us more quickly to the U.S. Supreme Court, where this nonsense will stop and we will win," said Brian Brown, president of the National Organization for Marriage, which opposes same-sex marriage. "There is no constitutional right to redefine marriage. It is pretty simple."

David Boies, co-counsel for the plaintiffs seeking to overturn Proposition 8, said Tuesday's decision marked "a great day for Americans who care about equality."

"This vestige of state-sponsored discrimination and second-class citizenship will be removed from the constitution of our state," Boies said.

Boies and co-counsel Ted Olson said the U.S. Supreme Court could issue a landmark ruling on gay marriage by June 2013 if justices agree to hear the appeal.

The California case is one of two gay marriage cases likely to be appealed to the Supreme Court this year. The other involves the federal Defense of Marriage Act, a 1996 law that denies tax, Social Security and other federal benefits to gay and lesbian couples who are married legally in their home states.

Last week, the 1st U.S. Circuit Court of Appeals, based in Boston, struck down a major portion of DOMA, ruling it was unconstitutional because it unfairly denies federal benefits to legally married same-sex couples.

The Obama administration, on the same grounds, has refused to defend the federal law. House Republicans hired Washington attorney Paul Clement to carry on the defense, and he has vowed to appeal.

A week earlier, a federal judge in Oakland ruled against portions of DOMA that prevented the California Public Employees' Retirement System from extending long-term care insurance to same-sex partners of California workers. That ruling, too, is expected to be appealed.

"What this means now is everything is in front of the Supreme Court," said UC Davis law school professor Vik Amar.

Despite the appeals, experts said it's not certain the high court will agree to take up both cases. Amar predicted the justices would "proceed incrementally" and likely start with the Defense of Marriage Act before granting or denying review of the Proposition 8 case.

He said the Supreme Court could reject consideration of Proposition 8 because the 9th Circuit ruling was narrowly drawn, focusing on California law and ignoring the broader question about whether same-sex couples may ever be denied the right to marry.

But he said the high court may feel compelled to rule on Proposition 8 because "California is not like any other state."

"People in the rest of the country have to pay attention to what we do in California because we are the most important state economically, socially and demographically," he said.

Leslie Gielow Jacobs, a constitutional law professor at Pacific McGeorge School of Law, said the Supreme Court may be unwilling to take on the gay marriage issue unless there are conflicting rulings at the circuit court level.

"I'm not really sure the justices want to step in and rule on this. It is so involved in the political process and such a rapidly evolving political issue."

Still, she said, "It's historic to have two circuit court rulings on gay marriage. It wasn't on the table 10 years ago."

Proposition 8, approved by California voters by 52-48 percent in November 2008, was overturned by U.S. District Judge Vaughn R. Walker in August 2010 on the grounds it violated equal protection and due process rights for gays and lesbians.

In February the 9th Circuit panel took issue with the state initiative process. In the majority decision, Judge Stephen Reinhardt wrote: "The People may not employ the initiative power to single out a disfavored group for unequal treatment and strip them, without a legitimate justification, of a right as important as the right to marry."

In Tuesday's ruling, three of the 9th Circuit judges vehemently dissented with the majority's refusal to grant a review of the February decision.

Judges Diarmuid F. O'Scannlain, Jay S. Bybee and Carlos T. Bea joined in a dissent written by O'Scannlain. They cited, in part, President Barack Obama's announcement last month that he supports same-sex marriage and would like to see the "conversation continue in a respectful way."

"Today our court has silenced any such respectful conversation," O'Scannlain wrote, adding: "Even worse, we have overruled the will of seven million California Proposition 8 voters. … We should not have so roundly trumped California's democratic process without at least discussing this unparalleled discussion as an en blanc court" review by the 9th Circuit.

Thirty-one states have approved measures banning gay marriage, and a voter referendum overturned legislation to legalize same-sex marriage in Maine. Legislators and court rulings have legalized same-sex marriage in eight states.

Since Proposition 8's passage, public opinion has shifted, with national polls showing growing acceptance of same-sex marriage. In California, a recent Field Poll of registered voters showed 59 percent to 34 percent support for permitting same-sex marriage.

Boies said acceptance of same-sex marriage appears inevitable amid a changing landscape for gay rights, including repeal of the military's "don't ask, don't tell" policy.

"There has been a tremendous shift," Boies said. "It is clear where this country is headed. We are now in a place where the question is no longer 'if' but 'when.' "

Calling the 9th Circuit's decision "a gross misapplication of the law," Brown of the National Organization for Marriage said he expects the Supreme Court to step in on the side of California voters and the gay marriage ban.

"With a case of this magnitude and so much at stake, I have no doubt the Supreme Court is going to take this on," he said.

Editor's note: This story was changed June 6 to correct the spelling of Leslie Gielow Jacobs' middle name.

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