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

The 52-to-48-per-cent tally Wednesday morning came with more than 95 per cent of the precincts reporting, and threw into doubt the more than 18,000 same-sex unions that have already taken place in the state.

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

San Francisco city attorney Dennis Herrera said he would lodge a legal appeal against the amendment on the grounds that it was unconstitutional. Gloria Allred, an attorney for the first gay couple to wed in the state, also said she would appeal the amendment.

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 - most of whom backed Democratic 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 youth 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 the Yes on 8 campaign. "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," wrote blogger Michael O'Hare.

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)