SAN FRANCISCO - The California Supreme Court voided the nearly 4,000 same-sex marriages sanctioned in San Francisco earlier this year, a move that will likely spur a new round of litigation about whether California's Constitution allows the weddings.

The seven justices on Thursday all said Mayor Gavin Newsom's decision to issue the licenses and perform the ceremonies violated a 1977 state law that defines marriage as a union between a man and woman.

The justices separately decided with a 5-2 vote to nullify the 3,995 marriages performed between Feb. 12 and March 11, when the court halted the weddings.

The court focused its ruling on the limits of local government authority, and did not resolve whether the California Constitution would permit a same-sex marriage. That question will have to wait as a flurry of lawsuits and countersuits over the gay weddings rise through the state's courts.

Chief Justice Ronald George, writing for the majority, noted that Thursday's ruling doesn't address "the substantive legal rights of same-sex couples." Instead, it insists that local officials can't legislate state law from city halls or county government centers.

Anti-gay-marriage groups hailed the ruling.

"Instead of helping his cause, Mayor Newsom has set back the same-sex marriage agenda and laid the foundation for the pro-marriage movement to once and for all win this battle to preserve traditional marriage," said Mathew Staver, who represents Campaign for California Families in its lawsuit.

Attorney General Bill Lockyer, who challenged the city's gay marriages directly to the Supreme Court, said that he regards it "as a ruling that simply says rule of law, rule of law, rule of law. That's how we govern our society."

But Newsom was defiant at a news conference at City Hall, where he appeared with city officials, many of them gay and lesbian, and spoke to a number of couples who he had allowed to get married. He said his "heart was heavy" that the marriages were voided, but vowed to carry on the city's constitutional challenge.

The justices said when they agreed to hear the case that they would entertain a challenge arguing that gays should be treated the same as heterosexual couples under the California Constitution, if ever such a lawsuit reached the high court.

Gay and lesbian couples immediately took up their invitation, were countersued, and the cases were consolidated. Legal briefs are due in September, and the Supreme Court won't likely hear the case for another year.

The wedding marches have prompted several anti-gay marriage efforts in statehouses and ballot boxes nationwide. Missouri voters this month endorsed a state constitutional amendment banning same-sex marriage.

Louisiana residents are to vote on the same issue Sept. 18. Arkansas, Georgia, Kentucky, Mississippi, Montana, Oklahoma, Oregon and Utah are to vote Nov. 2. Initiatives are pending in Michigan, North Dakota and Ohio.