By Tom Brooke in New York

George Clooney has been careful with his anti-war statements

Celebrities are proving to be the most powerful voice against a possible US attack on Iraq, surpassing the efforts of the Democrat Party to be President Bush's most vocal opposition.

They are marching in the streets, appearing in TV commercials - and in the case of Sean Penn they have even�visited Baghdad.

The message from many Hollywood celebrities is that Saddam Hussein can be contained - there is no need for President Bush to lead a pre-emptive strike.

The chorus of showbiz dissent has been a noisy one.

Some, like actor Danny Glover, have been extreme in their opinions. His anti-war rhetoric questions US intentions in Iraq, and he claims the threatened attack is a sign of an expansionist America.

"Who is going to be the master on this planet, who is going to determine what other people do and say and it starts with Iraq, but it goes on and on and we have to stop it here," Glover said.

Sean Penn is claiming the Hollywood blacklist has returned

Others have been more careful. Uppermost in the minds of many activist stars is the lesson of Jane Fonda, who in 1972 travelled to North Vietnam. Many back in the US saw it as a treasonable visit.

Even after a very public apology she is still - to this day -� trying to live down the title of 'Hanoi Jane'.

Actor and director George Clooney, another opponent of war, has said "it's dangerous when actors talk about it 'because unless you're really well versed on the subject, it could do more damage".

Sean Penn was wary of being cast in the same light as Fonda on his recent fact finding mission to Baghdad. This month he filed a lawsuit and said the Hollywood blacklist had returned.

He has alleged a producer dropped him from a role because of his trip to Iraq and opposition to war - the producer has filed a countersuit in which Penn has been described as "crazy and irrational".

'Political morons'

Conservative commentators have not been shy in attacking the celebrities' views.

"They are proving they are political morons," says conservative talk show host Bob Grant.

"All of a sudden they want us to take them seriously as pundits as though they are informed, as though they are wise in the ways of the world and it's ludicrous."

Stars are irked by this criticism - feeling that because they are celebrities they are not qualified to comment.

Jane Fonda drew controversy over her North Vietnam visit in 1972

The anti-war protests, however, are more vocal than any opposition from the Democrats.

But even the most conservative commentators have expressed admiration for the way the ant-war movement has marshalled celebrity support.

"I think the peace movement has been rather clever in using celebrities - even the stupid ones to open issues and get airtime on talk shows," said pundit John Leo.

"That is shrewder�of them than many Americans understand," he said.

At film festivals, at major awards such as the Grammy the drumbeat of anti-war celebrity protest makes itself heard. Anti-war rhetoric is now expected at the Oscars - but will it make any difference?

"I very much doubt it," says Todd Gitlin, professor of journalism at Columbia University.

"They have very much decided that Hollywood has gone over to the enemy."