Film star Arnold Schwarzenegger announced this evening that he will be a candidate in California's recall election this fall, a decision that startled political leaders across the state and immediately transformed the already tumultuous campaign.

For the past two weeks, Schwarzenegger had allowed his top advisers to suggest that he was strongly leaning against running on the recall ballot as a potential successor to Gov. Gray Davis (D) if voters remove him from office. But the Hollywood icon kept his intentions private until an appearance late today on NBC's "The Tonight Show With Jay Leno."

"The man who has failed the people more than anyone is Gray Davis. He has failed them terribly," Schwarzenegger, a Republican, told Leno. "This is why I'm going to run for governor."

Later, he told reporters that he intends to restore California's "disastrous" finances and challenge the influence that he said special interests have on the state's government. He also said he will fund his campaign only with his own money. "I will go to Sacramento, and I will clean house," he said.

Schwarzenegger's surprise move came on another dizzying day of political maneuvering in California over the historic recall. To Davis's great relief, Sen. Dianne Feinstein (D) said she will not be a candidate in the race. But author and columnist Arianna Huffington declared her candidacy, in response to pleas from liberal activists in the state who disdain Davis almost as much as the conservative Republicans who have led the recall movement.

Feinstein, who has been under growing pressure to run by Democratic leaders who fear Davis will lose the recall and cost the party control of California, issued a statement calling the Oct. 7 election a "terrible mistake" that will destabilize the state. "I hope as the next two months unwind, the frivolous nature of this recall will become more apparent," she said, "as well as the dark repercussions sure to follow."

Meanwhile, Huffington, who some Democratic strategists say could collect votes that Davis badly needs to survive in office, denounced the recall as a "right-wing power grab" but also called it a gift to voters. "However corrupt the parentage of the recall," she told supporters in Los Angeles, "it has given us an unprecedented opportunity to take back our political system." She will run as an independent.

Schwarzenegger's entry into the historic election changes every calculation that political strategists have been making about it. He becomes the first moderate Republican in the race. His candidacy almost surely means that former Los Angeles mayor Richard Riordan, his close friend and Republican ally, will not run. The film star's presence could greatly overshadow the campaign of Rep. Darrell Issa (R), who spent $1.7 million of his fortune bringing the recall movement to life. And strategists in both parties said Schwarzenegger's candidacy is likely to put new pressure on Democrats to field an alternative to Davis, who is the first governor in the country in more than 80 years to face a recall vote.

Many Republicans, and some Democrats, believe that Schwarzenegger instantly becomes the most formidable candidate in the race because of his celebrity, his wealth and his reportedly moderate views on many political issues. He also will be running as a political outsider at a time when polls suggest that many California voters, in the throes of the state's severe budget crisis, are exasperated with both Democratic and Republican leaders.

It was unclear tonight whether Schwarzenegger had a last-minute change of heart about running, or had engineered an elaborate ruse to fool Davis and other candidates who are contemplating campaigns into thinking they did not have to worry about him.

Schwarzenegger had dropped hints all summer about his ambition to be governor, and had assembled an informal campaign team that had been taking polls and polishing his stands on a range of issues. But his aides also had said repeatedly that he was unlikely to run because his wife, television journalist and Kennedy family member Maria Shriver, was objecting to the burdens a campaign would impose on their family. They have four children.

After his appearance with Leno, Schwarzenegger told reporters that his decision to run was "the most difficult decision of my life. I felt in the end it was my duty to jump into the race. People are sick and tired of politicians." He also said that Shriver, a Democrat, had told him she would stand by whatever decision he made.

Tonight, Democratic leaders appeared to be divided over the impact of Schwarzenegger's candidacy. Some said his presence in the election gives even more strength to their claim to voters that it has become a circus. "This thing is just nuts," said Roger Salazar, a political adviser to Davis. "Arnold has name recognition -- but some polls have found that a big part of the electorate does not take him seriously."

Other Democratic strategists have said that Riordan posed more of a threat to Davis because Schwarzenegger is untested on the campaign trail and for the first time will have to answer serious questions on issues, his finances and even allegations of womanizing that have been raised in the entertainment media in recent years.

But Schwarzenegger's candidacy may increase Democratic calls to put an alternative to Davis on the ballot before Saturday's deadline for candidates to enter the race. The governor and his allies are struggling to keep the party unified behind him. Polls are suggesting that a majority of voters are inclined at this point to support the recall.

Hours before Schwarzenegger's announcement, Democratic officials said that Lt. Gov. Cruz Bustamante (D) had been sending signals today that he is going to launch a campaign. One party official said tonight that it is "highly likely" Bustamante will run.

Some Democratic leaders say they doubt the governor can recover politically before the recall vote. Polls show that Davis's approval ratings have declined below 25 percent amid California's budget crisis. But this week Davis won the backing of all nine Democratic candidates for president as well as national and state labor leaders -- some of whom threatened political retaliation against any Democrat who enters the election.

Feinstein said today that she did not run because she believes that Davis and the Democratic Party can beat the recall. But in a conference call with reporters, she criticized the campaign Davis is waging against it, saying that he needs to show voters he is working forcefully on their behalf -- and not just denounce the recall as a right-wing conspiracy.

"That's a failed strategy from the get-go," Feinstein said.

Staff writer Dan Balz contributed to this report.

Arnold Schwarzenegger with Jay Leno on "The Tonight Show." To announce his bid for California governor, the actor used the show, which functions as a forum for the famously political. Story, Page C1. Actor Arnold Schwarzenegger discusses his campaign plans with reporters after announcing he will run.