By Steve Schifferes BBC News Online Washington correspondent

The US anti-war movement is stepping up its protests in a "pre-emptive strike for peace," amid fears that the Bush administration is moving rapidly to authorise US forces to attack Iraq.

On Saturday thousands of demonstrators are expected to converge on Washington DC, for a peaceful demonstration and a march on the US Navy Yard to demand the inspection of weapons of mass destruction.

The protesters are a broad-based coalition

And the peace movement plans a series of local demonstrations against the war in cities across the US on 29 January, the day after President George Bush delivers his annual State of the Union address to Congress. There will be another march and rally in New York City in February.

Among those speaking out against a possible war in Iraq on Saturday will be actress Jessica Lange, former US Attorney General Ramsay Clark, and the injured Vietnam war veteran Ron Kovic, who told of his growing opposition to that war in the book and movie Born on the 4th of July.

From the heart

Mr Kovic told BBC News Online he believed that he was seeing the growth of a new movement that would dwarf the size of the Vietnam War protests, and represented a "revolutionary transformation" in America as important as the Revolutionary War of 1776.

Ron Kovic has spoken in the UK at anti-war protests

He said the peace movement was non-violent, and was addressing people's "hearts and souls" as it aimed at broader social changes and the rebirth of democracy.

He said that it would show the world a different, more compassionate side of America that would "erase the stain" of an aggressive war.

And he said he wanted to give meaning to his own wartime sacrifice by helping stop the war this time before it begins.

He also called for close cooperation between US and UK peace movements, not just to work against the war, but to mobilise for social change.

Race against time

Brian Becker, a spokesman for A.N.S.W.E.R (Act Now to Stop War and End Racism), the organiser of the march, said the peace movement was engaged in a race against time to win the battle for public opinion before the war started.

This was contested by White House spokesman Ari Fleischer, who said equal or larger numbers of Americans supported the president's approach to Iraq.

President Bush will not be at the White House during the demonstrations, but will be preparing his State of the Union address at his weekend retreat at Camp David, Maryland.

So far public opinion polls suggest that there is conditional support for a war against Iraq, but confusion about its motivation and fears about US casualties.

According to the Pew Research Centre, two-thirds (68%) of the American public favour the use of force to remove Saddam Hussein from power, but only 26% support unilateral military action by the US.

If the war resulted in thousands of US casualties, then military action is opposed by 48%, with only 43% in favour.

And more than half of respondents (53%) say that President Bush has not explained clearly why it is necessary to use force to end Saddam Hussein's rule.

The anti-war coalition says the expected war is neither necessary or just, and is aimed at securing US oil supplies in the Middle East.

But they are trying to expand their appeal by campaigning on domestic political issues as well as the war.

Broad-based coalition

Many of the organisers believe there is a link between the expected war on Iraq and the lack of money for social programmes at home.

Youth and student coordinator Peta Lindsay said that the money that was going for the US military should be spent on schools and colleges instead.

The anti-war movement sees one of its strengths as the fact it is a "rainbow coalition," working with African-Americans, Hispanics, and immigrants, and reflecting their concerns with the Bush Administration, which recently signalled its opposition to affirmative action.

One activist, Larry Holmes, cited the words of Martin Luther King during the Vietnam War protests, that the "bombs falling on South-East Asia are exploding in the ghettos of America."

And the anti-war coalition is certainly broader than the Vietnam War coalition was at a similar stage - including elements of the US labour movement and many religious leaders.

But whether it will have the same amount of time to fully mobilise its supporters remains to be seen.