Thursday's unanimous decision, written by Chief Justice Tani Cantil-Sakauye, strongly affirmed that ballot sponsors may represent California in defending initiatives when elected officials fail to do so. Gov. Jerry Brown and Atty. Gen. Kamala D. Harris have refused to challenge last year's federal ruling against Proposition 8.
Legal scholars said the state high court's decision was so adamant that the U.S. Supreme Court, which could decide marriage rights as early as 2013, was unlikely to limit its ruling to the narrow and technical issue of "standing," a legal term for the right to go to court.
"It's a gangbusters opinion," said Santa Clara University law professor Gerald Uelmen, an expert on the state high court.
"This makes such a strong case that the sponsors represent the state and can represent the state's interests that it pretty much seals the deal," he said.
Advocates for two same-sex couples who challenged Proposition 8 in federal court said Thursday that they expected the U.S. 9th Circuit Court of Appeals to rule no later than February on the constitutionality of the 2008 ballot measure, which banned same-sex marriage.
The 9th Circuit indicated last December that it was leaning toward finding Proposition 8 unconstitutional if the standing issue was resolved. But such a decision would probably be appealed to the U.S. Supreme Court.
The 9th Circuit's ruling will affect all Western states within its jurisdiction. If the U.S. Supreme Court upholds marriage rights, its decision would benefit gays even in states like New York where same-sex marriage is already legal, activists said.
In asking the California Supreme Court to clarify the right of sponsors to defend Proposition 8, a three-judge panel of the 9th Circuit said it would abide by the state court's decision.
Thursday's ruling was a defeat for gay rights groups, which argued that ProtectMarriage had no standing to appeal U.S. District Judge Vaughn R. Walker's ruling last year that found the state's same-sex marriage ban unconstitutional. The groups contended that only elected state officials could appeal.
But Jennifer Cunningham, a New York coordinator of several gay rights groups, said the California Supreme Court decision would accelerate federal review of marriage rights, and "a rising tide lifts all boats."
The California court's decision was also a setback for state officials, who had insisted that they had the exclusive right to defend ballot measures in court.
In a terse statement, the attorney general noted that the court had disagreed with her but expressed certainty that "justice will prevail" in the federal courts. Seven national polls during the last year have reported majority support for same-sex marriage.
ProtectMarriage celebrated the ruling, contending that it signaled the demise of the Proposition 8 lawsuit.
"This ruling is a huge disaster for the homosexual marriage extremists," said Andy Pugno, an attorney for ProtectMarriage.
"The court totally rejected their demands that their lawsuit to invalidate Proposition 8 should win by default with no defense," he said.
"Their entire strategy relied on finding a biased judge and keeping the voters completely unrepresented. Today that all crumbled before their eyes."
Several gay rights groups expressed disappointment.