California voters haven't changed their minds about Republican candidates for governor since last winter, a poll released Thursday indicates.

The Field Poll shows former eBay Chief Executive Officer Meg Whitman and former congressman Tom Campbell are virtually tied with about half the voters undecided. State Insurance Commissioner Steve Poizner is still a distant third.

On the Democratic side, state Attorney General Jerry Brown leads San Francisco Mayor Gavin Newsom by a large margin.

Brown, who hasn't formally announced his candidacy is the preferred candidate of 47 percent of Democratic voters, up from 26 percent in March. Newsom's support is 27 percent. They were the only two Democratic choices.

Newsom is favored by younger voters, while Brown is far ahead with older voters. Brown is one of the most recognizable politicians in the state with favorable ratings in his current job and as mayor of Oakland, although he left the governor's office in 1983 with only a 43 percent approval rating.

Nearly half the state's Republicans have no opinion about the two leading Republican candidates, which is seen as good news since both Whtiman and Poizner are wealthy self-financed candidates who can spend heavily on advertising.

The poll surveyed 1,005 registered voters between Sept. 18 and Oct. 5, including 496 Democratic primary voters and 373 Republican primary voters. No margin of error was given.