SAN FRANCISCO — San Francisco's attempt to legalize same-sex marriages, which made the city a magnet for gay and lesbian couples from around the nation and the focus of a nationwide political uproar, ran into a roadblock Thursday at the California Supreme Court.

The justices ruled unanimously that Mayor Gavin Newsom overstepped his authority when he ordered the marriage licenses issued on Feb. 12 in defiance of a state law that defines marriage as a union between a man and a woman.

By a 5-2 vote, the court ruled that none of the 3,955 couples that flocked to City Hall in response to Newsom's decree was ever legally married or entitled to the rights of spouses. The court said their $82 license fees should be refunded.

"A same-sex marriage performed in violation of state law is void and of no legal effect," said Chief Justice Ronald George, rejecting the city's plea to leave the couples' status unresolved until the court decides the validity of the marriage law in a future case.

Jeri Tafoya, 39, of Salt Lake City, was disappointed to learn her marriage to Carmen Melendez, 36, was nullified, even though she knew it had no legal value in Utah, where same-sex marriages are not recognized.

"It's just one more stab in the back," Tafoya said. "Everything we do just to get basic rights is such a fight. I hate feeling like a second-class citizen in our state."

Tafoya said the couple drove all night to get to San Francisco, arriving at 4 o'clock in the morning.

"I stood in line for 11 hours on the 22nd of February, the rain was pounding like crazy," she said. "So many other people had waited 25 years."

Michael Mitchell, executive director of Equality Utah, said even though the marriages were strictly symbolic for roughly a dozen Utah couples, "it was still very meaningful for them."

Bill Wilson, who married his partner of 13 years at San Francisco City Hall in February, said the decision made him angry but determined. Wilson, 54, said he considers the judgment "a speed bump on the road to equality" and he will continue to consider his marriage legal.

"We were 10th in line to register for domestic partners in 1991 and first in line to get married," Wilson said. "You can't invalidate what's in my heart."

But George said Newsom's claim of authority to disregard a law he considered unconstitutional would set a dangerous precedent, allowing local officials to defy state statutes on civil rights, environmental protection and gun control based on their personal interpretations of the Constitution.