San Francisco Mayor Gavin Newsom shook up the California gubernatorial race Friday by dropping his struggling bid for governor, leaving Democrats with no declared candidate for the top statewide office.

Attorney General and former Gov. Jerry Brown has opened an exploratory committee for governor but has yet to formally announce his candidacy.

Nonetheless, Brown has built a wide lead over Newsom in both fundraising and in the polls, including winning the support of unions across the state and the country.

In a statement released Friday afternoon, Newsom cited the time demands of running a gubernatorial campaign while serving as mayor and caring for a 6-week-old baby daughter as his reason for leaving the race.

"With a young family and responsibilities at city hall, I have found it impossible to commit the time required to complete this effort the way it needs to – and should be – done," Newsom said.

"This is not an easy decision. But it is one made with the best intentions for my wife, my daughter, the residents of the city and county of San Francisco, and California Democrats."

Newsom, 42, had billed himself as a younger alternative to the 71-year-old Brown and boasted of innovative San Francisco initiatives, including its universal health care and green energy programs.

Newsom won national attention in 2004 by allowing same-sex marriages to be performed in his city. He also became the butt of jokes after admitting to an affair in 2007 with the wife of his re-election campaign manager.

Brown has been the Democratic front-runner for months although he has done no campaigning and insists he hasn't made a final decision yet about whether he'll run.

Political analysts said Newsom's departure was a boon to Brown, who can avoid a primary fight if he announces his candidacy and save his ammunition for what promises to be a costly general election.

Two of the three Republican gubernatorial candidates, former eBay CEO Meg Whitman and state Insurance Commissioner Steve Poizner, are wealthy former executives who can throw millions of their own dollars into their campaigns. Former Silicon Valley congressman Tom Campbell is also seeking the GOP nomination.

In a written statement Friday, Brown said of Newsom's departure from the race, "Mayor Newsom is a talented public official, and I believe he has a bright future. I am sure this was not an easy decision. (Wife Anne Gust) and I wish Gavin and his family all the best."

Newsom's departure could clear the way for another Democrat to jump in as the more liberal alternative to Brown, said Mark Baldassare, president of the nonpartisan Public Policy Institute of California.

Democratic Reps. Jane Harman, D-Venice, another millionaire, and Loretta Sanchez, D-Anaheim, have been mentioned as possible candidates.

Harman declined to comment Friday about the gubernatorial race.

"Newsom was filling the more progressive portion of the party, younger voters, more progressive voters, and that would seem to be an area that there might be opportunity for candidates," Baldassare said.

Brown's hefty war chest and name identification, however, could prove a deterrent, said former state Sen. Sheila Kuehl, who had endorsed Newsom.

"Anybody would have to think twice about challenging him," Kuehl said. "Gavin had been working for quite a while in building his support. He got Bill Clinton and a number of other good people, and still made the calculated decision that it wasn't going to work, and he didn't want to waste the resources."

Rumors of Newsom's departure had circulated for weeks, especially after a much-publicized Clinton endorsement last month failed to produce a substantial bump in contributions to Newsom.

Before the Clinton event, Brown raised nearly $7 million from January 2008 to June 2009 while Newsom had raised $2.9 million in the same period. Meanwhile, Newsom had spent $1.8 million on his campaign, while Brown had spent only $370,935.

Despite the lack of campaigning, Brown enjoyed a 20-point lead over Newsom in a Field Poll released this month. Brown also widely led all three Republican candidates, while Newsom claimed slim leads over the Republicans.

Newsom's campaign co-chairman Alex Padilla said Friday's announcement had nothing to do with money or poll numbers.

About Brown's lead in the polls, Padilla said, "It's early in the campaign, and there was still time to close the gap."

Padilla, a Democratic state senator from Los Angeles, also said about Brown's fundraising advantage, "We never needed to outraise Jerry. We just needed to raise enough to be competitive."

Democratic political consultant Bill Carrick said running for governor is a job with "24-7 demands."

"The fundraising is just literally being trapped in a room calling donors all the time," Carrick said. "There are very few people that are willing to do that. And it's all the more complicated if you're a sitting mayor. … You're at it all day, all the time."

Call Jack Chang, Bee Capitol Bureau, (916) 326-5543. The Bee's Steve Wiegand, Jim Sanders and Amy Chance contributed to this report.