LOS ANGELES  There is little suspense over the presidential race here, but a ballot initiative to overturn gay marriage is garnering the attention of politicians, activists and big spenders.

Proposition 8, which would amend California's constitution to define marriage as between a man and a woman, was put on the ballot after a state Supreme Court ruling in May said a ban on gay marriage was unconstitutional.

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The ruling triggered a rush to the altar by gay and lesbian couples, including many from other states seeking legal recognition of their unions. That prompted what has become a pricey and exuberant battle.

"This is the most expensive cultural war in America, ever," says John Duran, a West Hollywood City Council member and fundraiser for opponents of Prop 8. "It's a cultural war over the role of gay and lesbian Americans in California."

Opponents of same-sex marriages are determined to trump the court at the ballot box and have unleashed a massive campaign of organizing, television ads and fundraising.

Their early success at fundraising forced gay-marriage advocates to step up their own campaign efforts, and now the two sides are on track to spend more than $60 million, about evenly divided. The issue has made impromptu demonstrations a common sight across Southern California, as people from both sides wave signs at motorists from suburban street corners.

California's record as a trend-setter for the rest of the nation means the implications go beyond the borders of a state that is home to roughly 12% of the nation. While similar issues face voters in Florida and Arizona, both sides believe victory here is of paramount importance to shape public attitudes about same-sex marriage nationally under the next administration.

"This is the second-biggest race in the country," says Sonja Eddings Brown, spokeswoman for the Yes on 8 campaign. "And the impact of Proposition 8 is going to set a precedent for the United States of America."

Despite a tendency to elect Republican movie stars as governor, California has become reliably Democratic in presidential races. President Bush lost here twice, by 11 percentage points in 2000 and 10 in 2004.

This year, Republican John McCain has campaigned little in the state even though it offers the largest prize of all the states, 55 electoral votes.

An Oct. 25 Rasmussen Reports poll showed Obama leading 61%-34%.

California TV viewers have seen a deluge of ads on Prop 8. Ads supporting the amendment warn that schoolchildren "will be taught about gay marriage unless we vote yes on Prop 8."

The other side responds with commercials featuring the state's top educator, Superintendent Jack O'Connell, saying the issue has nothing to do with schools or kids. "Our schools aren't required to teach anything about marriage, and using kids to lie about that is shameful," he says.

The Yes on 8 campaign points to education officials who feel it should be taught. And it cites the example of Massachusetts, where the state Supreme Court legalized gay marriage in 2004. A federal appeals court ruled in February that the state can deny parents the right to remove their second-graders from classes that required reading books such as King and King, which is about two princes marrying.

The charges have stirred grass-roots campaigning by people who aren't normally involved in campaigns. William Adams, 51, of Irvine has festooned his Chevy pickup with hand-drawn wooden signs urging a vote for Prop 8 and declaring it a matter of parents' rights to control what kids are exposed to.

Adams says he fears his church, the Church of Jesus Christ of Latter-day Saints, could be sued for discrimination for not recognizing gay couples.

"We're not afraid of the homosexual movement; We are afraid of the government," Adams says.

He has planted more than 50 yard signs and led groups of others in knocking on doors for votes for Prop 8. The door-to-door canvassing, as well as telephone voter-turnout efforts, are organized by his Mormon ward, or local church, Adams says.

Brown, the spokeswoman for Yes on 8, estimates 40% or more of the $28 million the group reported raising by Oct. 18 had come from Mormon donors. But she says the coalition to overturn gay marriage is broad and even includes groups that tend to vote Democratic.

"We expect turnout in the African-American community to be an asset to us," she says.

Geoff Kors, a member of the executive committee of the No on 8 campaign, says, "Every poll suggests this is a dead heat."

Brown hopes that after Tuesday, gay marriage will be history in California. "We really are at a cultural crossroads in America where we are going to be forced one way or another to decide whether the rights of children or the rights of gay adults are going to come first," Brown says.