Aug. 12 (Bloomberg) -- The California Supreme Court ruled San Francisco Mayor Gavin Newsom didn't have the authority to issue wedding licenses to same-sex couples and voided more than 4,000 gay marriages the city performed earlier this year.

The decision preserves a ban on same-sex nuptials in California that the court ordered in March while it reviewed challenges from the state and groups opposed to the practice. State law defines marriage as between a man and a woman.

San Francisco captured national attention earlier this year for issuing marriage licenses to gay couples. Massachusetts is the only state that has legalized same-sex weddings. President George W. Bush has called for a constitutional amendment to bar gay marriage.

``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 Matt Staver, a lawyer who represents the Campaign for California Families, a group that challenged the weddings.

Newsom, 36, scheduled a press conference for later today. He declined to comment before the conference, Bob Lipman, a spokesman for the mayor, said in a phone interview.

The California Supreme Court focused only on the question of whether Newsom had authority to issue the marriage licenses. Whether California laws banning gay marriages are constitutional is being considered in trial courts and won't be reviewed by the high court for another year or two.

`Important Question'

``The real important question remains completely unanswered, which is whether limiting marriage to one man and one woman violates the Constitution,'' said Bradley Joondeph, assistant law professor at Santa Clara University, in an interview before the court issued its ruling.

California Attorney General Bill Lockyer, representing the state in the marriage cases, said the ruling was ``an affirmation of the duty'' that city officials have ``to obey the law.''

``I think it's disappointing for'' gay couples whose marriages will be annulled, Lockyer said. ``This isn't a fight we picked.''

The court decision that Newsom overstepped his authority was unanimous. Two justices dissented on whether the existing marriage licenses should be voided.

`Extremely Confident'

``At least two justices were persuaded that there was no need to invalidate the weddings while the broader constitutional issues worked their way through the court,'' San Francisco City Attorney Dennis Herrera said in an interview. ``We are extremely confident in our position and we believe that ultimately we are going to be successful.''

Californians approved Prop. 22, called the ``Defense of Marriage Act, in March 2000, which amended the state Family Code to state that only marriage between a man and a woman is valid or recognized in California. The measure was approved by 61 percent of the state's voters.

The cases are: Lockyer v. City and County of San Francisco, S122923, and Lewis v. Alfaro, S122865, California Supreme Court.

To contact the reporter about this story: Karen Gullo in San Francisco at kgullo@bloomberg.net

Last Updated: August 12, 2004 15:05 EDT