The decision "is specifically looking at the role of Proposition 8 in the California context," said Santa Clara University law professor Margaret M. Russell. Because it is limited to California, the Supreme Court may not be as concerned about reviewing it as it would a ruling that would have affected the entire country, she said.

"The opinion holds that Prop. 8 was unconstitutional only in a case where the state had already granted full legal rights to same-sex couples," said University of Minnesota law school professor Dale Carpenter.

If so, that would leave for another day — perhaps several years in the future — a national ruling on same-sex marriage.

The narrow California-only approach adopted by the 9th Circuit means the high court might choose to steer clear of the dispute.

Until Tuesday, it looked like California's Proposition 8 gay marriage case would be decided by the U.S. Supreme Court. But that looks less certain now.

Several state courts have struck down bans on same-sex marriage based on their state constitutions, but the U.S. Supreme Court has not ruled on whether such a ban denies gays and lesbians the "equal protection of the laws" under the 14th Amendment.

Indeed, the 9th Circuit's opinion reads as though its intended audience was one -- Justice Anthony Kennedy -- and its message was that there was no need for the Supreme Court to decide the California case.

Appeals court judge Stephen Reinhardt, a staunch liberal, did not say gays and lesbians have an equal right to marry under the Constitution. Instead, he said California's voters violated the Constitution by "taking away from them alone" the right they had won to marry under a state Supreme Court decision.

His opinion relies almost entirely on a 1996 opinion written by Justice Kennedy, the court's crucial swing vote.

That case arose when Colorado's voters adopted a state initiative that voided a series of local ordinances and state laws that protected gays and lesbians from discrimination based on sexual orientation. At that time, the high court had never ruled in favor of gays on a discrimination claim.

But in Romer vs. Evans, Justice Kennedy wrote a strong opinion saying the Colorado law was unconstitutional because it singled out gays and lesbians for unfair treatment and took away their hard-won legal rights. Kennedy did not say, however, that states must adopt gay rights laws.

Reinhardt's opinion repeatedly cites Kennedy's opinion. "Prop. 8 singles out same-sex couples for unequal treatment by taking away from them alone the right to marry," he said, including one of many citations to Romer vs. Evans.

The defenders of Prop. 8 have 90 days to appeal this decision directly to the Supreme Court and ask the justices to review it. But to win, they almost certainly would need the vote of Justice Kennedy.

The court's four conservatives — Chief Justice John G. Roberts Jr. and Justices Antonin Scalia, Clarence Thomas and Samuel Alito — could vote to hear the case. It takes only four votes to hear an appeal. But it takes five to have a majority.

Douglas NeJaime, a Loyola Law School professor of sexual orientation law, agreed that the ruling was written for Kennedy, but suggested that if the Supreme Court did take up the case, Kennedy could side with the four liberal justices to "find Proposition 8 unconstitutional without having to significantly expand their jurisprudence" -- meaning that it wouldn't have any effect on other states' gay marriage bans.

Alliance Defense Fund attorney Brian Raum said the Proposition 8 supporters hadn't yet decided whether to ask that a full 11-judge panel of the 9th Circuit reconsider the case or take their request for review and reversal directly to the U.S. Supreme Court.

The justices in Washington accept only about 1% of the cases appealed to them each year. Analysts were divided over whether the high court would grant review of the Proposition 8 ruling, with some saying the time is ripe for the justices to weigh in on whether there is a constitutional right to marry a same-sex partner and others seeing the 9th Circuit ruling as so narrowly tailored to the California case as to require no review.

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-- David Savage in Washington, Carol J. Williams in Los Angeles and Maura Dolan in San Francisco

Photo: Opponents of Prop. 8 celebrate outside of the U.S. 9th Circuit Court of Appeals on Tuesday in San Francisco. Credit: Justin Sullivan / Getty Images