KEY POINTS:
Republican Fred Thompson has said he has dropped out as a US presidential candidate, following a dismal showing so far in the campaign.
Meanwhile, presidential candidate Hillary Clinton holds a 12 point lead over Barack Obama among Democrats likely to vote in California's February 5 primary, according to poll results released overnight.
Thirty-nine per cent said they would vote for Clinton, the senator from New York, and 27 per cent said they would vote for Obama, a first-term senator from Illinois, the survey conducted by The Field Poll showed.
Since December, each of the leading candidates has gained ground by pulling voters from John Edwards, who now polls at 10 per cent, and other candidates.
A relatively large number, 20 per cent, remain undecided.
Voters who ranked health care, jobs and the economy as the campaign's most important issues were most likely to favour Clinton, whose lead is largest among women, Latinos and lower-income voters.
Voters who ranked the Iraq war and foreign policy as the most important issues were most likely to favour Obama, who is preferred by blacks, college graduates and Democratic primary voters with household incomes of US$80,000 ($105,932) or more.
Both candidates are highly regarded by three-quarters of the Democratic voters, but 58 per cent said Clinton has the right experience for the presidency.
The Field Poll spoke to 377 registered voters likely to vote in California's Democratic primary election. The voters were contacted by phone between January 14 and January 20. The survey's margin of error was per cent.
Fred Thompson
* Thompson, 65, who served as a federal prosecutor and Senate Watergate counsel in 1973 and 1974, won a special election to a two-year Senate term in 1994 and was re-elected to a full six-year term in 1996.
* Before being elected to the Senate, Thompson had roles in 18 feature films, including The Hunt for Red October, and In the Line of Fire.
* He returned to acting after leaving Congress and starred online at http://blogs.reuters.com/trail08/
- REUTERS
