SAN FRANCISCO (Reuters) - The biggest California gay rights advocacy group on Wednesday said it needed three years to build a coalition to repeal a ban on same-sex marriage in the state, creating a rift in the movement with those who want to go back to the polls next year while anger is hot.

Gay couple Ethan Collings (L), 32, and his spouse Stephen Abate, 36, hug as they celebrate their one-year wedding anniversary in West Hollywood, California, June 16, 2009. REUTERS/Lucy Nicholson

California, the most populous state and often a standard-bearer for social liberalism, is the biggest prize in U.S. culture wars. Its next fight over gay marriage is sure to draw in national organizations, cost $100 million or more, and may affect the next U.S. presidential campaign if it takes place in 2012.

California’s November 2008 vote to ban same-sex marriage, months after the state’s top court legalized it, bolstered the power of social conservatives and sparked nationwide protests among gays and their allies. It was followed by legalization of gay marriage in a handful of mostly Northeastern states and a court challenge aimed at the U.S. Supreme Court.

“It takes time, commitment and lots of lots of volunteers to undo the untruths that our opponents have been telling,” said Marc Solomon, marriage director of Equality California, in a conference call. “We can have majority support by 2012.”

His group raised the most money and led the 2008 campaign against Proposition 8, which defines marriage as between a man and a woman and was approved by California voters.

Big donors are not ready to fund a new fight so soon after failure, and a door-to-door campaign will take time, he said. A bigger turnout in the 2012 presidential election year, as well as more younger voters, will add 4 percentage points to the margin of victory, the group estimated.

GRASS-ROOTS WON’T WAIT

But smaller groups have said waiting will sap momentum among gays and their allies still smarting from the unexpected ballot results. They vowed to mount a 2010 challenge, which would coincide with federal mid-term elections.

“This is not some kitchen table group. If you stop that momentum now, those people won’t necessarily be there in 2012 when you decide to start your campaign back up,” John Henning, executive director of Love Honor Cherish, said ahead of Equality California’s expected announcement.

Henning’s group has a plan to gather more than a million signatures with volunteers and says a $32 million war chest would be enough to win the fight.

The California debate reflects a national question over how solid opposition is to same-sex marriage. Many advocates say that exposure to stable same-sex couples and assurances that churches will not be forced to marry gays will convince a silent majority that anyone should be able to marry. But most states explicitly ban such gay unions, and have often done so by popular vote.

Activism among gay rights groups has intensified since the November defeat in California, but social conservatives with deep pockets and legendary organizational skills are preparing for the next fight, too.

“California will continuously stay in play and it is a big prize,” said Tom McClusky, vice president of the legislative arm of the Family Research Council, a conservative Christian lobby. “Of course we would be willing to go toe to toe again.”

ProtectMarriage.com, which helped coordinate passage of the ban, scoffed at the division among gay marriage advocates. “While the other side issues many press releases about their activity, we are quietly but effectively building on our majority in California,” it said in a statement.

Proponents of the 2010 challenge say the decision will be made from the bottom up and that big groups will join as a campaign plan is laid out and early efforts show success.

“We’re in a movement era,” said Rick Jacobs, who chairs the Courage Campaign, which trains grass-roots organizers. The day after the California ban passed -- and after President Barack Obama was elected -- was a wake-up call for gay advocates, he said.

“On the one hand they put an African American man in the White House when it was impossible. On the other hand they had their rights taken away.” He said his group has raised more than $100,000 in a few days for a fight to repeal the ban.

Equality California said it would take a lot more money and said gay marriage opponents were raising money faster in Maine, which is likely to vote on gay marriage in November.

“We are very concerned that $100,000 is not $50 million,” said Equality California Executive Director Geoff Kors, adding that he saw only one shot to win in the next two California elections.

(Additional reporting by Ed Stoddard in Dallas)