Most memorably, Ms Benjamin was one of two women seen directly behind Mr Rumsfeld at last month's congressional hearings on Iraq holding an anti-war placard and later charged with "disruption of Congress".

This Saturday, she will help lead what organizers hope will echo in scale the anti-war protests of the Vietnam era three decades ago.

"Opposition to the war seems to be mushrooming," said Ms Benjamin, founding director of Global Exchange, the San Francisco-based rights group and a Green party candidate for senator.

Ms Benjamin, who was also arrested when protesting in California during a presidential visit last month, said yesterday it was significant that the movement was gaining support at such an early stage: "We don't have a draft and there aren't any body-bags coming home.

"There has been a remarkable coming together of groups that normally wouldn't work together."

She said that after a "virtual blackout" by the national media, the events were being covered, "but it is still not the coverage one would expect".

Two big rallies are planned this Saturday, in San Francisco and Washington, which aim to bring at least 100,000 protesters onto the streets. Any smaller turnout, when compared to protests in Europe, including last month's in London, would be seen as "embarrassing", one Californian organizer said.

The protesters hail from ad hoc peace groups, student and religious organizations, liberal Democrats, leftwing parties, pacifist groups, relatives of September 11 victims and remnants of the anti-Vietnam war movement, including Ron Kovic, now 62, the paralyzed Vietnam war veteran who became a leading anti-war activist in the 1970s and whose story was told in the film Born on the Fourth of July, starring Tom Cruise.

Jesse Jackson, the former US attorney general Ramsey Clark and Scott Ritter, the one-time UN weapons inspector in Iraq who is vociferously opposed to a war, will address the Washington rally.

Although a Gallup poll this month showed that 38% of Americans oppose war in Iraq, within mainstream politics there has been a reluctance to speak out against the war, not least because of next month's mid-term elections and candidates' fears of being seen as unpatriotic.

Some well-known names are involved. A whole-page ad in the New York Times last month placed by Not In Our Name was signed by Jane Fonda, Susan Sarandon, Robert Altman, Marisa Tomei, Oliver Stone, Kurt Vonnegut, Alice Walker, Steve Earle, Claes Oldenberg, Gore Vidal and hundreds of others from the arts and academia.

On Friday, Sean Penn took out a large advertisement in the Washington Post to attack the war "as a father and an American".

More surprisingly, Business Leaders for Sensible Priorities, which includes Ben Cohen, co-founder of ice-cream company Ben & Jerry's and dozens of company presidents and chief executives, took a whole page ad in the New York Times. It showed President Bush, his vice-president, Dick Cheney, and Mr Rumsfeld under the slogan, "They're selling the war . . . we're not buying."