SACRAMENTO -- Meg Whitman, the former eBay executive who stepped onto the political landscape last year as an adviser to John McCain, is preparing to run for California governor in 2010, adding another big name to an increasingly crowded field of potential contenders.

She stepped down from the boards of eBay, Procter & Gamble Co. and DreamWorks Animation SKG as of Dec. 31, her spokesman, Henry Gomez, said Monday. He said it was for "personal reasons and time commitments" but would not elaborate.

A person who is knowledgeable about Whitman's political aspirations told The Associated Press that the 52-year-old Silicon Valley leader is planning to run for governor. The person, who spoke on condition of anonymity because he was not authorized to speak about her future on the record, said Whitman's resignations are "a strong indication" that she wants to clear any commitments that might interfere with a run for political office.

She will make the announcement official in four to six weeks, he said.

Whitman is one of three Republicans who are considered front-runners in the 2010 California gubernatorial campaign. The others are state Insurance Commissioner Steve Poizner and former Rep. Tom Campbell.

Gov. Arnold Schwarzenegger, a Republican, is prohibited from running again under the state's term-limits law and will leave office in January 2011.

Bruce Cain, a political science professor at the University of California, Berkeley, said Whitman's business background makes her a good choice for Republicans, although little is known about her ability to perform in public office or her social views. That creates a sense of uncertainty about her potential candidacy, he said.

"We also don't know where she fits into the spectrum of the Republican Party in California," Cain said. "My sense is she's very possibly in the mainstream on economic issues, but where is she on abortion, stem-cell research, gay marriage, benefits for domestic partners?"

If Whitman were to win the GOP primary, she is likely to face a well-known Democratic opponent in a state where registered Democrats outnumber Republicans by 13 percentage points.

Former Gov. Jerry Brown, 70, now the state's attorney general, is thought to be the leading Democratic candidate if he decides to run -- unless Sen. Dianne Feinstein jumps into the race.

Longtime Feinstein consultant Bill Carrick said Monday that the state's senior senator remained interested in running for governor, but it would be some time before she made a decision. She just became chairwoman of the Senate Intelligence Committee, providing motivation to stay in Washington, D.C.

He said Feinstein, 75, was being encouraged to run but that the Republican field wasn't much of a consideration.

"I don't think that Senator Feinstein's doing any kind of political handicapping of who the Republicans are going to run or not run," Carrick said.

San Francisco Mayor Gavin Newsom and Los Angeles Mayor Antonio Villaraigosa also are considered top Democratic contenders, especially if neither Brown nor Feinstein is in the race.

The GOP side of the race remains wide open. A November Field Poll found that between two-thirds and three-quarters of registered California voters had no opinion of the potential Republican candidates.

But the poll found that Whitman had the highest favorable rating among the three, at 23 percent.

Whitman retired last March after 10 years as chief executive at eBay. A billionaire, she retains a 2 percent ownership stake in the company.

Whitman's strategy will be to appeal to the growing segment of California voters -- nearly 20 percent of the electorate -- who are registered independent. The California GOP did not allow independents to vote in last year's presidential primary but will allow them to vote in the 2010 gubernatorial primary, party spokesman Hector Barajas said.

He said Republicans would get excited about a primary race pitting Whitman against Poizner, 52, a fellow moderate and Silicon Valley entrepreneur. Poizner, an electrical engineer, helped develop a GPS chip for cell phones and made a fortune when the company, SnapTrack, was sold for $1 billion in 2000.

"It would be a healthy campaign," Barajas said. "You're going to have two very strong individuals on the Republican side, two business-minded individuals who understand what it takes to provide one of the most important things we need in California -- and that's jobs."

Poizner has formed an exploratory committee, which declined comment Monday.

Whitman most recently served as a national co-chair of McCain's failed presidential campaign and previously had supported former Massachusetts Gov. Mitt Romney, who lost to McCain in the GOP primary. Whitman and Romney once worked at Bain and Co., a global business consulting firm. Romney later started Bain Capital, the venture capital firm where he made millions.

Whitman has donated money to candidates and causes in the past, but was not particularly active in state politics while she was in charge of eBay. Little is known about her social views.

She contributed $200,000 to Schwarzenegger's successful campaign last year to create a bipartisan commission to redraw California's legislative districts, according to state campaign finance records.

Whitman supported Proposition 8, the gay marriage ban that also passed in November, according to the source who is familiar with her political aspirations. There is no indication that she contributed money to the campaign, according to a review of campaign finance records.

Over the past few years, she has supported Republican and Democratic candidates, including Schwarzenegger and former state Controller Steve Westly, a Democrat who lost in the 2006 gubernatorial primary. Westly is a former eBay executive.

A Democratic strategist said Whitman will find a difficult environment for Republicans if she decides to run for governor.

Bob Mulholland, spokesman for the California Democratic Party, said the state has not fared well under Schwarzenegger and noted that Whitman backed McCain, who lost to President-elect Barack Obama in California by 24 percentage points. It was the widest margin in a presidential contest in California since World War II.

"Meg took a pretty big beating," Mulholland said. "If she thinks she can pay to be loved by California voters, she'd be making a big mistake."

He said Whitman could join Democrat Al Checchi and Republican Bill Simon as wealthy business people who failed in their bids for California governor. Checchi lost to fellow Democrat Gray Davis in the 1998 primary, while Simon lost his challenge to Davis' re-election in 2002.