Updated

Sen. Dianne Feinstein on Wednesday said she would not run for governor of California, complicating things for state Democrats who want a strong candidate should Gov. Gray Davis  lose his Oct. 7 recall vote.

"After thinking a great deal about this recall, its implications for the future, and its misguided nature, I have decided that I will not place my name on the ballot," the Golden State Democrat said in a statement.

In a major boost for Davis' efforts to keep the governor's mansion, Feinstein said he should be given the chance to finish his second term. Davis won re-election last November.

Several Democrats, including three other members of Congress, had publicly urged Feinstein to run, saying the party needed a backup candidate in case Davis lost his job.

"I am very flattered by the many elected officials, community leaders, and constituents who have urged me to put my name on the recall ballot as insurance should the recall be successful," Feinstein said in her statement.

Feinstein, 70, tops opinion polls as the state's most popular politician, and many analysts believe that if she ran, Davis' chances of survival would plummet.

Feinstein called the recall a "terrible mistake that will bring to the depth and breadth of California instability and uncertainty, which will be detrimental to our economic recovery and decision-making.

"This sets a terrible precedent which ought to cause us all to think very carefully."

Feinstein has served in the Senate since 1992, two years after narrowly losing the gubernatorial election to Republican Pete Wilson (search). She defeated a recall attempt when she was mayor of San Francisco in 1983.

Feinstein's popularity, her desire for the state's top job — and a frosty relationship with Davis — were the main reasons several Democrats had publicly urged her to run.

On Tuesday, the AFL-CIO (search) backed Davis, calling on Californians to oppose the recall and urging Davis' fellow Democrats to keep their names off the ballot.

"We call on all state leaders in the Democratic Party to stand united with the governor," according to a resolution adopted by the powerful labor federation's Executive Council.

Feinstein's decision, coupled with the AFL-CIO's support, were incremental victories for Davis, whose support from fellow party members had been crumbling.

Sen. Barbara Boxer said Monday she strongly opposed the recall, but felt that Democrats should field another candidate if polls show Davis will lose his job.

Sources told Fox News that California Democratic leaders were "still searching for an alternative ... a backup."

On Monday, Rep. Loretta Sanchez said she believed the Democrats would field an alternate to Davis even if Feinstein decided not to run.

The deadline for candidates to file candidacy papers is 5 p.m. Saturday. More than 300 people have expressed interest in running.

The two-part ballot Oct. 7 will ask whether voters want to remove Davis from office and list candidates to replace Davis should the recall succeed.

Feinstein pointed out that most of the proclaimed or presumed candidates knew next to nothing about running the nation's largest state.

The next governor will have to manage the state's $99 billion severely overstrained budget, fill judgeships and other state posts, oversee law enforcement and homeland security efforts and meet the challenges facing California's public schools.

"This is a time when our attention should be focused on working in a bipartisan manner to solve the state's fiscal crisis, to fix our public schools, to increase public safety and to restore California's economy," Feinstein said. "Sadly, the state is instead going to be engaged in an election that is becoming more and more like a carnival every day."

On the Republican side, state Sen. Tom McClintock of Thousand Oaks filed his candidacy papers Tuesday. Rep. Darrell Issa (search), who bankrolled the recall drive, has said he will be a candidate.

Former GOP congressman and Senate candidate Michael Huffington was considering a run, and Huffington's ex-wife, political columnist Arianna Huffington (search), announced her candidacy on Wednesday's "Today" show. She said she would run as an independent.

"Out of chaos comes an incredible opportunity to focus on the real problems of California," Huffington said. "My main goal will be to galvanize people — people who have given up on politics."

Fox News' Adam Housley and The Associated Press contributed to this report.