The U.S. Supreme Court today paved the way for same-sex couples to marry soon in California, effectively leaving intact a lower-court ruling that struck down the state’s voter-approved ban on gay marriage.

In a ruling that assures further legal battles, the high court found that backers of Proposition 8 did not have the legal right to defend the voter-approved gay marriage ban in place of the governor and attorney general, who have refused to appeal a federal judge’s 2010 ruling finding the law unconstitutional.

The Supreme Court ruling, which found it had no legal authority to decide the merits of a challenge to Proposition 8, sends the case back to that original decision — and the only question now is how quickly same-sex couples can marry and whether that ruling will have immediate statewide effect.

Gov. Jerry Brown said the state will instruct county clerks across California to start issuing marriage licenses to gay and lesbian couples once the Supreme Court’s decision is final and the legal details are complete in the lower courts. Attorney General Kamala Harris has advised the governor that the original injunction against Proposition 8 applies statewide, which would compel the state to issue marriage licenses to same-sex couples once the Supreme Court’s ruling becomes final, ordinarily in about 25 days.

But Proposition 8 supporters maintain former Chief U.S. District Judge Vaughn Walker’s 2010 ruling only applies at most to two counties, Alameda and Los Angeles, despite the fact he blocked state officials from enforcing Proposition 8 at the time. Andrew Pugno, ProtectMarriage.com‘s chief lawyer, vowed to try to limit the scope of Walker’s ruling when the case returns to the lower court, but the group is still “reviewing all of its legal options.”

Among other arguments that can be raised, he added, is a provision in the California constitution that requires state officials to enforce ballot measures unless an appeals court declares it unconstitutional. Tuesday’s 5-4 ruling, written by Chief Justice John Roberts wipes out last year’s 9th U.S. Circuit Court of Appeals decision finding Proposition 8 unconstitutional because the ballot measure’s supporters never had the legal right to appeal Walker’s 2010 opinion.

Proposition 8 has remained in force in California while the case has been unfolding in the courts, but Harris said she will urge the 9th Circuit to the end a stay of Walker’s injunction put in place while the case has been on appeal “as quickly as possible.” And lawyers for the same-sex couples challenging Proposition 8 also indicated they will try to get same-sex marriages moving forward in California faster than the usual protocol in the aftermath of Supreme Court decisions.

A 9th Circuit spokesman, however, said the appeals court typically waits for the 25 days before taking any further action. The three-judge panel handling the case has not taken any additional steps thus far to accelerate the case in response to the state attorney general.

In an interview with Bay Area News Group, Walker said Wednesday the Proposition 8 case was always clouded by the issue of whether the measure’s supporters could defend the law alone. The former judge added that there is no ambiguity in his view that his injunction applies statewide.

“But my mind doesn’t control this,” Walker said.

With its narrow approach to California’s circumstances, the Supreme Court left for another day the broader question of whether any state has a right to outlaw gay marriage.

The Supreme Court found that it did not have the legal authority to go that far in the Proposition 8 case.

“We have never before upheld the standing of a private party to defend the constitutionality of a state statute when state officials have chosen not to,” wrote Roberts, joined by an odd coalition of Justices Antonin Scalia, Stephen Breyer, Elena Kagan and Ruth Bader Ginsburg. “We decline to do so for the first time here.”

The Supreme Court also struck down a 1996 federal law denying benefits to same-sex couples, a major victory for gay rights advocates seeking the right to marry. In a 5-4 ruling written by Justice Anthony Kennedy, the high court found the 1996 Defense of Marriage Act unconstitutional because it violates the equal protection rights of same-sex couples. Kennedy also dissented in the Proposition 8 case, saying the Supreme Court had the ability to decide the challenge to the California law without the defense of state leaders.

“DOMA’s principal effect is to identify a subset of state sanctioned marriages and make them unequal,” Kennedy wrote, referring to same-sex marriages in states that have moved to permit gay marriage.

Writing in dissent, Scalia warned that the DOMA ruling would become fodder to groups challenging state bans on gay marriage, saying the issue should be left to the political battles unfolding across the country.

“By formally declaring anyone opposed to same-sex marriage an enemy of human decency, the majority arms every challenger to a state law restricting marriage to its tradition definition,” Scalia wrote.

The Supreme Court’s decision in the DOMA case immediately provides full federal benefits to same-sex couples in the 12 states that have legalized gay marriage, and would apply in California with Proposition 8 overturned. It also would provide federal benefits to the more than 18,000 same-sex couples married in 2008 before Proposition 8 was passed.

The decision was welcome news for Karen Golinski, a San Francisco attorney who had an identical challenge to the federal law on hold in the Supreme Court awaiting the decision in a case out of New York. A federal judge previously declared the law unconstitutional in Golinski’s case, which involved a challenge to the federal government for denying health benefits to her spouse, Amy Cunninghis. The couple married before Proposition 8 went into effect.

“We’re ecstatic,” Golinski said after the ruling. “It was a very moving decision and it has a profound effect on us as a couple. The majority’s decision understood that.”

The Supreme Court’s much-anticipated rulings come at a time when the nation’s views on the controversial gay marriage issue have shifted considerably. Twelve states permit gay marriage, and politicians from President Barack Obama to three Republican senators have come out in favor of permitting gay and lesbian couples to wed.

The Obama administration, in fact, took the unprecedented step of urging the Supreme Court to find both Proposition 8 and the federal Defense of Marriage Act unconstitutional.

In California, a Field Poll earlier this year showed 61 percent of voters back gay marriage, much stronger support than when 52 percent of voters approved Proposition 8 five years ago and a profound change from 1996, when Congress passed the federal law denying equal marriage benefits to same-sex couples. At that time, the public was overwhelmingly against gay marriage.

The Supreme Court’s decision in the Proposition 8 case punctuates the state’s nine-year struggle over gay marriage, which began in 2004 when former San Francisco Mayor Gavin Newsom tried to skirt California’s ban on same-sex nuptials by issuing marriage licenses to gay and lesbian couples at city hall.

That short-lived maneuver, blocked by the California Supreme Court, spawned the first legal conflagration over same-sex marriage rights in the state. In that case, the state Supreme Court in May 2008 struck down California’s previous laws banning gay marriage, paving the way for more than 18,000 couples to marry before voters approved Proposition 8 in November and restored the same-sex marriage ban.

Those same-sex marriages were left intact, and, with the overturn of DOMA, the couples now are entitled to full marriage benefits.

A Los-Angeles-based organization, backed by civil rights activists and Hollywood types such as director Rob Reiner, moved in early 2009 to overturn Proposition 8. Suing in San Francisco federal court on behalf of two same-sex couples, including Berkeley’s Kristin Perry and Sandy Stier, the group argued that California’s same-sex marriage ban is unconstitutional because gay and lesbian couples are denied the same marriage rights offered to heterosexual couples.

Perry and Stier said Wednesday they were “elated” by the ruling and look forward to getting married once the legal case is over, although they expressed hope gay marriage rights would be extended to couples nationwide eventually. The legal challenge set up an unprecedented test of a state’s right to outlaw gay marriage, crafted by an unlikely powerhouse duo of famed trial lawyer David Boies and Theodore Olson, the conservative former U.S. Solicitor General during the Bush administration. Bodies and Olson had squared off against each other in Bush v. Gore, but teamed up to force the U.S. Supreme Court to eventually tackle the gay marriage issue.

In early 2010, former federal judge Walker held a three-week trial in which Proposition 8 backers defended the law without any help from California’s top officials. Walker later declared the law unconstitutional, in the process becoming the target of gay marriage foes when he publicly revealed he was in a long-term same-sex relationship, a fact that had been well-known in Bay Area legal circles.

The 9th U.S. Circuit Court of Appeals upheld Walker last year, albeit in a narrower ruling that found Proposition 8 unconstitutionally stripped away the previous right to marry in California without any justification. That led to the Supreme Court’s intervention in the case.

The Proposition 8 case has been clouded by a number of legal intricacies, notably whether the ballot measure’s sponsors even have a right to defend the California law in lieu of Gov. Jerry Brown and Attorney General Kamala Harris, who consider it unconstitutional.

The Supreme Court heard arguments in the Proposition 8 and DOMA cases in March. The challenge to the federal law was pressed by Edith Windsor, an 84-year-old New York woman who was denied equal estate benefits when her spouse and partner of 40 years died in 2009, costing her hundreds of thousands of dollars in taxes that a heterosexual married couple would not have to pay.

Howard Mintz covers legal affairs. Contact him at 408-286-0236 or follow him at Twitter.com/hmintz