The 52-year-old political neophyte began testing her affinity for politics after leaving the online auction site after 10 years last January. She served as finance chairwoman for Mitt Romney’s presidential campaign and then as a national co-chair of John McCain’s.

“California faces challenges unlike any other time in its history – a weak and faltering economy, massive job losses and an exploding state budget deficit,” Whitman said in a statement on her Web site. “California is better than this, and I refuse to stand by and watch it fail.”

She said former Gov. Pete Wilson will be her campaign chairman.

Whitman will face Insurance Commissioner Steve Poizner, another wealthy former Silicon Valley executive, and former Rep. Tom Campbell, in the Republican primary. Gov. Arnold Schwarzenegger, a Republican, is prohibited from running again under the state’s term-limits law and will leave office in January 2011. His moderate social and fiscal positions have often put him at odds with the state Republican Party and the Bush administration.

Whichever candidate emerges from the GOP field will face a stiff challenge in the 2010 general election as the party continues to lose voters. Republicans accounted for 31.4 percent of registered voters last November, a slide of more than 3 percentage points since the 2004 elections. The party, which has grown more conservative in recent years as California voters have become more centrist, has been shedding voters for more than a decade as the ranks of independents in California has grown.

President Barack Obama defeated Republican challenger John McCain by 24 percentage points last year, the widest margin in a California presidential race since World War II.

Nevertheless, Poizner’s communications director, Kevin Spillane, said Whitman’s decision is a sign of strength for the state GOP.

“Campaigns are about differences and we look forward to Meg Whitman and other Republican candidates joining Steve Poizner in a vigorous discussion about who has the hands-on experience, innovative ideas and conservative instincts to save California,” Spillane said in a statement.

Whitman promoted her financial experience during the presidential campaign but has not revealed her positions on social issues such as abortion, stem-cell research and the death penalty. She supported the gay marriage ban approved by California voters in November.

The Republican nominee will face a crowded Democratic field that is expected to include former governor and current Attorney General Jerry Brown, San Francisco Mayor Gavin Newsom, Los Angeles Mayor Antonio Villaraigosa and Lt. Gov. John Garamendi. Sen. Dianne Feinstein has not said whether she will run or remain in Congress.

The 52-year-old Republican plans to run in 2010 for the seat Gov. Arnold Schwarzenegger is leaving but is not ready to make a formal announcement, said the person, who was not authorized to talk publicly and spoke Monday on condition of anonymity.

Whitman made the decision while spending time with family over the holidays and will make the announcement official in four to six weeks, he said.

Henry Gomez, a spokesman for Whitman, said she stepped down from the boards of eBay, Procter & Gamble Co. and DreamWorks Animation SKG last week due to “personal reasons and time commitments.” He would not elaborate.

The person who said Whitman is planning a gubernatorial run said her resignations are “a strong indication” that she wants to get clear of any commitments that might interfere with a run for political office.

In a statement, John Donahoe, eBay’s president and chief executive, praised Whitman’s tenure at the head of the online auctioneer.

“Meg’s vision and leadership and her passion for the eBay community have helped create economic opportunity for millions of people worldwide and enabled us to build a dynamic portfolio of leading online businesses,” he said. “Her experience and insights will be missed, but Meg will always be a part of the eBay family, and we wish her the very best.”

Whitman retired in March after 10 years at the helm. A billionaire, she retains a 2 percent ownership stake in eBay.

She most recently served as a national co-chairwoman of John McCain’s failed presidential bid 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 led eBay. Little is known about her social views.

Whitman supported Proposition 8, the gay marriage ban that passed in November, according to the person who spoke about her political decision. Campaign finance records do not indicate she contributed money to that campaign.

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.

Whoever wins the GOP primary will face a well-known Democratic opponent in a state where registered Democrats outnumber Republicans by 13 percentage points.

Former Gov. Jerry Brown, 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 that 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.

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

Term limits prevent Schwarzenegger, a Republican, from running again.