California governor's race tightens - poll

* Survey shows Meg Whitman with slim lead over Jerry Brown

* Whitman also widens lead over Republican rival

By Steve Gorman

LOS ANGELES, March 17 (Reuters) - Ex-Governor Jerry Brown, the presumed Democratic nominee in California's gubernatorial race, has seen his lead over Republican front-runner Meg Whitman evaporate, according to a Field Poll of likely voters released on Wednesday.

Brown, the state attorney general who held double-digit leads over Whitman in Field Poll surveys taken in October and January, now trails the former eBay Inc (EBAY.O) chief executive by 43 percent to 46 percent in a two-way matchup.

Eleven percent of those polled, a random sample of 748 likely general-election voters, said they were undecided. Whitman's lead was within the statistical margin of error.

But the results mark a sharp turnaround in a race likely to pit a veteran politician who served two previous terms as governor against a billionaire business executive who has never sought public office and rarely even voted.

The poll also spells trouble for Democrats in a state where they strongly outnumber Republicans in voter registration and have lost few statewide races in the past 15 years, except for Arnold Schwarzenegger's election as governor in 2003.

"This is a blue state, a very blue state," said Field Poll director Mark DiCamillo. "We appear to have a Republican who can become competitive in this state, and I find that fairly remarkable given the changing demographics of the electorate."

Whitman also widened her advantage over her rival for the Republican nomination, state Insurance Commissioner Steve Poizner, 63 percent to 14 percent. In January, she led Poizner 45 percent to 15 percent. The percentage of undecided Republican voters shrank from 38 percent to 23 percent.

Brown, not surprisingly, still holds a better-than three-to-one lead (69 percent to 20 percent) over Whitman among Democrats. But Whitman's lead among registered Republicans is even greater, 77 percent to 13 percent.

Registered nonpartisans -- now accounting for one in five California voters -- split heavily in favor of Whitman over Brown, 50 percent to 36 percent.

Whitman also holds huge leads over Brown among the roughly one-third of likely California voters who identify with the Tea Party movement. She scored better among middle-aged and older voters, who make up the lion's share of the electorate, while Brown was favored by younger and ethnic voters. Both male and female voters preferred Whitman by small margins.

By comparison, Brown led Whitman last October 50 percent to 29 percent, but saw his lead shrink to 10 percentage points, 46 percent to 36 percent, in January.

Brown, a three-time presidential contender who served eight years as governor starting in 1975, only officially launched his campaign on March 2 to succeed Schwarzenegger, who is barred by term limits from running again.

Whitman, meanwhile, has spent heavily on television campaign ads for months that appear to have helped her make key gains in Los Angeles County, representing about a quarter of the electorate, DiCamillo said. (Editing by Dan Whitcomb and Philip Barbara)