Political earthquakes abound in California, from the recall election that put Republican action figure Arnold Schwarzenegger in the governor's office to San Francisco's gay marriages. It's uncertain ground for even the most sure-footed presidential candidates.

The nation's most populous and ethnically diverse state is also the most valuable turf on March 2. That day, 10 states hold elections worth more than half of the 2,162 delegates needed to nominate the Democratic candidate, with California offering the largest prize -- 370 delegates

John Kerry (search), the undisputed front-runner, will make California just one part of a national March 2 strategy. But underdog John Edwards (searchis targeting the state as one of four he hopes to win -- with Ohio, Georgia and New York -- to keep his candidacy alive.

"It's an uphill climb, but we wouldn't be coming here if we didn't think he could do very well here," said Edwards spokesman Roger Salazar, a longtime California political veteran. "We really do think his message of optimism, of lifting people up, resonates well here."

Edwards, who will spend 2 1/2 days campaigning across California beginning Wednesday, will aim his populist economic themes toward voters still reeling from the dot-com bust that bled thousands of jobs from the state. Aides say he will also speak out forcefully on the environment -- a hot issue in California, where President Bush's policies, including plans for oil drilling off the state's pristine coast, have angered many voters.

But polls show Edwards needs to make up significant ground. A Los Angeles Times poll released Tuesday showed Kerry holding a commanding lead over Edwards -- 56 percent to 24 percent -- among the state's likely voters.

Kerry is counting on his front-runner status and a string of topflight endorsements to propel him to victory.

"Our primary thrust will be outreach to elected officials, constituency groups, and activists," said Larry Grisolano, Kerry's state director. "California's diversity and key industries like technology have great symbolic importance to us."

Kerry has the backing of the state's senior U.S. senator, Dianne Feinstein, as well as state treasurer Phil Angelides and Los Angeles City Councilman Antonio Villaraigosa, a popular figure among the state's Hispanic voters.

Kerry will meet Edwards and the remaining Democratic candidates for a debate in Los Angeles Thursday evening and will campaign in the state on Friday.

With television advertising prohibitively expensive in California -- as much as $5 million a week for a full-blown media effort -- neither Edwards nor Kerry is likely to rely on air time to carry their messages. Instead, both are counting on favorable news coverage and outreach to supporters of candidates who have left the race -- most notably Howard Dean, who had an enthusiastic California organization.

"The perception is that Kerry is the nominee, and it's going to be hard for Edwards to overcome that," said Democratic strategist Kam Kuwata. "But the television coverage is very helpful for Edwards -- he is an energetic, personable candidate and California voters are as susceptible to television coverage as anyone else."

Both candidates will almost certainly be pulled into the debate over San Francisco's recent decision to grant marriage licenses to same-sex couples, a wedge issue both had sought to avoid. President Bush raised the political stakes Tuesday in embracing a constitutional amendment to ban gay marriage.

Kerry and Edwards oppose gay marriage, although Kerry was one of only 14 senators to vote against the Defense of Marriage Act (search) in 1996. The law denied federal recognition of same-sex marriages licensed in individual states.

Calling the matter a "state issue," Kerry said Bush is wrong in trying to amend the Constitution. "All Americans should be concerned when a president who is in political trouble tries to tamper with the Constitution of the United States at the start of his re-election campaign," the Massachusetts senator said in a statement.

Kuwata said that while Kerry remains the presumptive favorite in California, he would do well to emulate the state's political rock star, Schwarzenegger.

"What's important is that Kerry communicates energy and that his message is one of optimism," Kuwata said. "Californians see Schwarzenegger that way -- he seems to bring people together to solve a problem. I think the electorate here is looking for something much more than anger."