(CNN) - Eight months before California's primary, a new poll suggests that Jerry Brown, the state's sitting attorney general and former governor, holds a 20-point lead over San Francisco mayor Gavin Newsom in the battle for the Democratic gubernatorial nomination.
The survey, by Field Research Corporation, indicates that the fight for the GOP nomination is up in the air, with nearly half of Republican primary voters undecided.
According to the Field poll, 47 percent of Democratic primary voters support Brown, while 27 percent back Newsom, with just over one in four undecided. Brown, who served two terms as California governor from 1975 to 1983, has not formally declared his candidacy.
The survey indicates Brown leads Newsom by 31 points in Southern California, but by just 5 points in the northern part of the state, where Newsom is better known. The poll also suggests a generational divide, wtih the much-younger Newsom leading by nine points among voters 39 and younger. According to the survey, Brown holds a 30-point advantage among voters age 40 to 64, and he has a 45-point lead among those 65 and older.
The poll indicates that the three GOP candidates are far less well-known than Brown or Newsom - which makes it understandable that 49 percent of California's Republicans are undecided in the race for their own party's gubernatorial nomination. Twenty-two percent say they support former eBay head Meg Whitman, with 20 percent backing former Rep. Tom Campbell and 9 percent supporting wins the support of State Insurance Commissioner Steve Poizner.
According to the survey, Brown holds significant, double-digit leads over each Republican candidate in hypothetical general election matchups. Newson is also ahead of each GOP hopeful, though the survey suggests his leads register in the single digits.
Term limits prevent the state's current governor, Republican Arnold Schwarzenegger, from running for a third term in 2010.
The California Field Poll was conducted September 18-October 5, with 1,005 California registered voters questioned by telephone. The survey's overall sampling error is plus or minus 3.2 percentage points.