The actor Warren Beatty has said he will not run for the US presidency this year as he fears that he might harm the causes he believes in.

In an interview with Vanity Fair magazine, he said the prospect of making a poor showing had prompted him not to enter the California and New Hampshire primaries.

The Hollywood actor, director and producer - active in Democratic Party politics for more than 30 years - said he feared his critics would say: "Look Mr Movie Star was up here and tried to do something with these issues and look how unpopular they are.

"One has to be very, very careful not to be an unwitting party to making what most people consider to be unfashionably liberal ideas appear to be more unpopular than they really are," he added.

"I think the question is: Can I be more effective at another time? Whether that is in a year or two years, who knows?"

Beatty said he feared that many of his concerns would be ignored, such as universal medical cover, action against exploitation of workers, rebuilding the school system and raising teachers' pay.

He also admitted that he was reluctant to make a fool of himself.

"I feel good about speaking up. I wouldn't feel good if I hadn't. It seems to me that the effect has been positive, that I've not yet made too big a fool of myself - at least I don't think I have."

Beatty has refused to endorse any candidate, including Vice President Al Gore and former New Jersey Senator Bill Bradley, who are vying for the Democratic Party's presidential nomination when the primaries and caucuses start in Iowa later this month.

"They're all good men, but none of them are saying enough of the things that need to be said," he said.

The actor, who wrote and starred in the 1998 political satire film Bulworth - about a senator who sold out to special interests - said he had become disillusioned with President Bill Clinton and the Democratic Party establishment.