BURBANK — Ending weeks of speculation, actor Arnold Schwarzenegger announced Wednesday that he will run for governor as a Republican so he can “clean up Sacramento.”

It was a day of major developments in the recall campaign. U.S. Sen. Dianne Feinstein put an emphatic end to efforts to get her to run, and Lt. Gov. Cruz Bustamante made a late-night announcement that he plans to enter the race, breaking ranks with Democratic efforts to prevent an intraparty challenger to Gov. Gray Davis.

But the most dramatic moment occurred during the taping of “The Tonight Show With Jay Leno,” where Schwarzenegger made his bombshell announcement. “The politicians are fiddling, fumbling and failing, and the man that is failing the people more than anyone is Gray Davis,” Schwarzenegger said. “He’s failing them terribly, and this is why he needs to be recalled. And this is why I’m going to run for governor of California.”

The news, which ran counter to most speculation about his intentions, was met with loud cheers from the studio audience.

Steve Smith, director of the pro-Davis group Californians Against the Costly Recall, dismissed the action movie star later as “one more name” on a growing list.

But Schwarzenegger’s entry instantly makes him the best-known candidate on the Oct. 7 ballot, and makes it all but certain that his friend, former Los Angeles Mayor Richard Riordan, will not run.

It also positions him as a nonpolitician who does not have to worry about fund raising, although he clearly could face severe personal attacks over claims of past drug use and boorish behavior toward women. “First of all, Larry Flynt is going to make me shine,” Schwarzenegger said of the Hustler magazine publisher, who also says he wants to run. “I know they’re going to throw everything at me and they’re going to say I have no experience, that I’m a womanizer, that I’m a terrible guy, and all these kind of things are going to come my way,” he said.

Schwarzenegger, who last week was said to have been backing away from the race, milked the attention up to the very last minute as hordes of reporters gathered at NBC studios. Even his closest advisers said as Schwarzenegger took the stage that they did not know what he had decided.

The scene took on the aura of a coronation at times, with hundreds of onlookers lining up around the building hoping to get into the show. A special media filing room with telephones was set up for reporters, and up until the end rumors swirled that Riordan would appear from the audience to announce for the job himself.

Schwarzenegger arrived at the studio about 4 p.m., and Leno joined him in the parking lot to show off a new motorcycle the talk show host had just purchased.

Later, meeting with reporters, Schwarzenegger said he planned to work against special interests in government.

“I will go to Sacramento and I will clean house,” Schwarzenegger said. “As you know, I don’t need to take money from anyone. I have plenty of money myself.”

Feinstein’s decision was overshadowed by the actor’s move, but still set off speculation over which Democrats might break ranks with Davis. Late Wednesday, Bustamante announced he would hold a 10 a.m. press conference at the Sacramento County Registrar of Voters office, where he will take out his candidacy papers to place his name on the recall ballot. In recent weeks he had repeatedly denounced the recall effort and said he would not run. As lieutenant governor he was responsible for setting the Oct. 7 election date. Aides would not elaborate on his reasons for changing his mind.

State Insurance Commissioner John Garamendi also is debating whether to run, adviser Darry Sragow said.

Congressional Democrats also continued their quest to find a candidate to appear on the ballot in case Davis loses the first part of the election, which asks voters whether the governor should keep his job. The second half lists replacement candidates.

Feinstein had been considered the ideal Democratic backup, but she made it clear Wednesday that she opposes the “misguided” recall effort and thinks Davis should keep his job. The move buoyed Davis’ spirits, who said he was “obviously pleased” at her decision, then lashed out at U.S. Rep. Darrell Issa, R-Vista, who helped fund the recall drive and now is running for governor.

“This was an effort by Darrell Issa, a right-wing Republican, to get to be governor,” Davis said in an interview on KFWB radio in Los Angeles.

Feinstein said she believes Davis can win, but she urged him to drop that campaign theme.

“He’s got to go out there and show people that he’s not part of the problem … ,” Feinstein said. “I don’t think the ‘right-wing conspiracy’ or anything like this works.”

Her decision left congressional Democrats in their second 90-minute conference call of the week debating who could be placed on the ballot as insurance against a Davis loss.

The most prominent elected members of the party have said they oppose the recall and will not run, but that stance appeared to be changing with Bustamante’s move and Garamendi’s internal debate.

“He’s been giving it some thought, and obviously we’re getting to crunch time,” Garamendi adviser Sragow said.

A handful of other Democrats still were positioning themselves, with U.S. Rep. Loretta Sanchez, D-Garden Grove, among those debating a run.

The moves were precisely what some party leaders had warned could lead to a crowded ballot, with several Democrats taking votes from one another.

“There’s going to be a jail break if one or more of those Democrats gets in,” said a gleeful Republican spokesman, Rob Stutzman.

By late Wednesday, the number of Californians who had expressed an interest in running had reached nearly 500, the secretary of state’s office reported. None has been certified as a candidate yet, and those who want to run have until 5 p.m. Saturday to pay the $3,500 fee and turn in the proper paperwork. Arianna Huffington, the 53-year-old ex-wife of former Republican U.S. Rep. Michael Huffington, joined the fray Wednesday at a campaign event at a youth center in south-central Los Angeles attended by 200 supporters.

“I’m not, to say the least, a conventional candidate,” she said. “But these are not conventional times.

“And if we keep electing the same kind of politicians who got us into the same kind of mess funded by the same kind of special interests, we’ll never get out of this mess.”