San Francisco - Six months after the California Supreme Court cleared the way for same-sex marriages in California, voters in the usually liberal state narrowly voted for a constitutional ban on gay marriage.

But defenders of same-sex marriage immediately filed three lawsuits, claiming the voter initiative improperly attempted "to undo the constitution's core commitment to equality for everyone by eliminating a fundamental right from just one group - lesbian and gay Californians."

The 52-to-48-per-cent vote in favour of the ban threw into doubt the more than 18,000 same-sex unions that have already taken place in the state since the court ruled that banning such marriages was discriminatory.

The measure was among the most closely watched ballot initiatives in the United States and was fuelled by a record 73 million dollars of spending during the campaign. Voters in Arizona and Florida also backed constitutional amendments banning gay marriage.

The lawsuits were filed by the American Civil Liberties Union, Lambda Legal and the National Center for Lesbian Rights; the counties of San Francisco, Los Angeles and Santa Clara; and an attorney for the first gay couple to legally wed in the state.

"The point of equal protection is that everybody is supposed to have the same rights, and minorities are protected against a majority that would abuse the minority," said Jenny Pizer, a lawyer for Lambda Legal.

The amendment was proposed by a broad coalition of religious and conservative groups whose main strategy was based on the argument that failure to pass it would lead to the teaching of gay marriage issues in the state's thousands of public schools.

That claim, repeated in TV ads replete with horror film music, disturbing black and white graphics and doom-laden voice-overs, was largely without factual merit. But it still reached its target audience in the state's conservative inland areas.

Just as importantly, it also appeared to persuade California's millions of black and Hispanic voters, who turned out in higher numbers to back Democratic presidential candidate Barack Obama but whose views on gay rights are less progressive than many other Democrats.

"Look at the Bible; it says marriage is between a man and a woman, not a man and a man," said Christopher Miracle, 19, a church-going black man from Oakland who said he voted for Obama.

"I think the story is that a strong majority of Californians support traditional marriage and they want to see it protected," said Frank Schubert, manager of a campaign to pass the proposition. "I think the story is we ran a far better campaign than the other side. I think we had 100,000 people that gave of their resources and their time."

Supporters of gay marriage said they were ashamed of the result but believed it would ultimately be overturned.

"I'm ashamed that more than half of my state's citizens are so ignorant or hateful or fearful or all three that they could do this," blogger Michael O'Hare wrote.

Commenting on the website of the San Francisco Chronicle, one reader warned proponents of the ban not to celebrate too much: "Look at the demographics: Young voters strongly support gay marriage. So to all of you who are cheering for Prop 8, chew on this: Your children and grandchildren will live in a world where gay marriage is legal."

On the streets of San Francisco's heavily gay Castro district, some gays were taking a philosophical attitude.

"I never took gay marriage as something that would stay in place because this country is so wound up about sex and marriage," Mike Cohn told the San Francisco Chronicle. "We need to be prepared to know that gay marriage can be taken away just as easily as it was given." (dpa)