SAN FRANCISCO, Aug. 6 - The recall election on Gov. Gray Davis of California went into an unpredictable freefall today, as one of the state's most respected elected officials, Senator Dianne Feinstein, announced that she would not run to replace Governor Davis, and Arnold Schwarzenegger, a politically untested movie star, announced that he would.

As extraordinary bookends on a day of fast-moving events, the two decisions could not have been more dissimilar in style and substance. Public opinion polls have identified Ms. Feinstein, a Democrat, and Mr. Schwarzenegger, a Republican, as among the most popular alternatives to the governor, who faces a recall vote on Oct. 7.

Even before Mr. Schwarzenegger's announcement late in the day, the day's developments, which also included the formal start of the candidacy of the columnist Arianna Huffington, had set off a panic among many of the state's elected Democrats.

Mr. Schwarzenegger, who has been spending most of the past weeks promoting his most recent ``Terminator'' movie, made his intentions known before a cheering television audience during a taping in Burbank, Calif., of ``The Tonight Show with Jay Leno.''

Instead of talking about issues like nuclear proliferation and appropriations, as Ms. Feinstein did, Mr. Schwarzenegger made light of his decision to run while joking with Mr. Leno.

But he did address the main question in the recall, saying: ``The man that is failing the people more than anyone is Gray Davis. He is failing them terribly, and this is why he needs to be recalled and this is why I am going to run for governor.''

Anxious members of the state's Democratic Congressional delegation held an urgent conference call, in which there was ``growing consensus'' that a Democratic alternative to Governor Davis must enter the recall race, one participant, Representative Cal Dooley, said.

``There is still time to identify another candidate, and I think that we are fortunate that we have a very deep bench of prominent Democrats in this state,'' Mr. Dooley said.

Ms. Feinstein, speaking from a foreign policy gathering in Aspen, Colo., said that she had decided Governor Davis deserved a chance to finish his term and that it was more important for her to carry on the business of the United States Senate than to delve into the recall. Governor Davis has strongly opposed the idea of a Democrat running on the so-called replacement part of the recall ballot.

Ms. Feinstein said she was appalled at the ``frivolity'' of the recall, which has attracted the interest of more than 400 possible candidates, from pornographers to idle millionaires, describing it as ``more like a carnival every day.''

``My hope is that this recall causes all of us in California to do some deep soul searching as to whether we really want it to be this way,'' Ms. Feinstein said in a telephone news conference.

Governor Davis, in a radio interview prior to Mr. Schwarzenegger's announcement, was asked about the prospect of running against him.

``The Terminator!'' the governor said on KGO-AM, ``I just don't want to comment. But let me just say this. People have rued the day when they said they want to run against someone. A lot of people have been excited about the potential of running against someone and found out that they turned out to be the ultimate loser in the contest. So be careful what you wish for in this business.''

Throughout the day, the disarray among the Democrats was palpable. The state party chairman, Art Torres and the chairman of the Democratic National Committee, Terry McAuliffe, who have stood by Governor Davis on the recall, canceled a news conference this afternoon just minutes before it was scheduled to begin.

The telephone conference call among the Democratic Congressional delegation lasted about 90 minutes and involved about half of its 33 members, Mr. Dooley said. Among the potential candidates most frequently mentioned during the discussion were Cruz M. Bustamante, the lieutenant governor, and Leon Panetta, a former California congressman and chief of staff to President Clinton, Mr. Dooley said.

Though both of those men have expressed opposition to the recall, and have indicated no intention to run on the replacement ballot, there was considerable speculation today that they might be open to a draft, particularly with the entry of a celebrity like Mr. Schwarzenegger.

Governor Davis and his supporters were dealt another potentially devastating blow when Senator Feinstein, in the telephone news conference, said that while she opposed a Democrat stepping in, she would not try to dissuade one from doing so.

``I don't see that as my role,'' Senator Feinstein said. ``I have said what I think about that. The only way to keep them off is to tie their hands behind their back so they couldn't' sign the papers.''

In the radio interview, Governor Davis reiterated his opposition to a prominent Democrat stepping in.

``To the extent that the Democrats get into the race, it makes it look like a normal election and legitimates what is really an effort by the right wing to steal back an election they couldn't win last November,'' Governor Davis said.

But with the deadline this Saturday for candidates to file as a possible successor to Governor Davis, some members of the state's Democratic delegation in Congress interpreted the timing of Senator Feinstein's announcement as a green light for them to search for a contender.

``There is growing apprehension about the ability of Governor Davis to defeat the recall,'' Mr. Dooley said. ``I think Senator Feinstein understands the interest among some of the Democratic leaders in California to consider other candidates for the recall and thus made her decision in order to allow consideration of the other candidates.''

Ms. Feinstein was also openly critical of Governor Davis's insistence on labeling the recall as a right-wing conspiracy. She said it was off the mark to characterize Representative Darrell Issa, the San Diego Republican who financed the signature gathering, as right-wing extremist.

She said Mr. Davis would only be able to defeat the effort to oust him if he began to talk about his strengths.

She also offered Mr. Davis some advice, saying: ``But I think the fundamental issue that is driving this, is people are disconcerted and are blaming the governor as the top official. He needs to go out there and show people he is part of the solution not part of the problem.''

At a news conference after his television appearance, Mr. Schwarzenegger also criticized the Davis strategy, which many Democratic consultants have predicted will only get nastier with Mr. Schwarzenegger in the race.

``He can run a dirty campaign better than anyone, but he can't run a state,'' Mr. Schwarzenegger said. ``In the end it is my duty to jump into the race and to bring hope to the people.''

When questioned by Mr. Leno, Mr. Schwarzenegger, a naturalized American citizen from Austria, said he had watched the state lose its luster.

``We are in a very disastrous situation right now,'' he said. ``When I moved to California in 1968, California was at the top of the greatest nation in the world. Everyone could come here and have opportunities. Now it is totally the opposite.''

Mr. Schwarzenegger, who has no political experience other than leading a successful statewide ballot initiative last fall on after-school programs, blamed California's politicians for its problems. The effort to oust Governor Davis has been largely fueled by unhappiness with the state's economic woes, which included a $38 billion budget deficit.

In an interview today in Aspen, where Senator Feinstein has spent the week attending a foreign policy conference and relaxing at her log home on a mesa overlooking the Aspen Valley, she said that she believed Mr. Davis could survive the recall, but she acknowledged that he faced an uphill battle.

``I think it is tough, but I think he can sustain a `no' vote on recall, if he lets people see him being decisive, solving problems, acting gubernatorial,'' she said. She said that she gave the question of running ``a lot of thought'' but decided in the end that her seniority in the Senate was too important to give up. ``So I am going to stay the course,'' she said.

Earlier in the day, Ms. Huffington, a populist author and syndicated columnist, officially announced her candidacy for governor. Ms. Huffington said she would not have entered the race if Senator Feinstein had decided to present herself as the Democratic alternative. ``I'm not interested in splitting the vote,'' she said.

A millionaire, Ms. Huffington said she would use none of her personal fortune for her campaign. Among her ideas for smoothing California's boom and bust budgets are closing tax loopholes and shelters for big corporations.

An independent, she made no bones about her disdain for both the Republicans and Democrats, calling them fanatics and fools.

``California is in deep, deep trouble,'' she said. ``Its citizens deserve more than the partisan, petty and pathetic leadership it's getting at the moment.''

David E. Sanger contributed to this article.