Demonstrators are mobilizing in Washington and cities across the country for what they consider their last chance to speak as one great multitude against the gathering clouds of an Iraq war.

The weekend demonstrations coincide with America's military buildup overseas and a time of remembrance for the nonviolent struggle embodied by the Rev. Martin Luther King Jr. Even as sailors ship out, protesters are packing Washington-bound buses and organizing local marches and vigils from Tampa, Fla., to San Francisco.

"We are attacking a poor country that has enough problems," said Al Svitesic, a retired pile driver and World War II veteran who will be rallying in Pittsburgh next week. "It is unjust."

The largest crowds are expected in the nation's capital, where President Bush and many in Congress are united on the move toward war and protest leaders hope they can draw tens of thousands, at least, to march in dissent.

"We've been working with protest groups; they've got permits for various locations, including marches, so we'll be ready for it," said Police Chief Charles H. Ramsey. "We don't anticipate any problems, although we do anticipate large crowds."

The organization International Answer planned the national rally Saturday in Washington and one in San Francisco, exhorting war opponents everywhere to "stop the Bush administration from threatening and killing the people of the world who are not our enemy."

The focus was on America's weapons of mass destruction, not the ones inspectors are looking for in Iraq in a possible prelude to conflict.

The sense that war is close, perhaps only weeks away, spurred the determination of many activists to get to Washington. This, despite a possible winter storm followed by a weekend of subfreezing temperatures in the capital.

Gerald Rudolph, director of a South Carolina group that sent one busload to the last large Washington rally, in October, said about twice as many people were going from his area.

"It's starting to reach visibility," he said of the anti-war movement. "Should we go to war, I think it'll just explode at that point." He leads the Carolina Peace Resource Center.

Nearly 500 people from Wisconsin signed up for bus travel to Washington. So did several hundred from upstate New York.

Ambitious weekend rallies are planned in Phoenix, in Portland, Ore., and in Tampa, where protesters plan to gather outside the headquarters of Central Command, the arm of the Pentagon that would direct the Iraq war. In Pittsburgh, activists are hoping to draw several thousand to Jan. 24-26 protests.

In San Francisco, the Internet-based group MoveOn.org released a TV commercial Thursday that depicts a girl plucking petals from a daisy and shows a nuclear mushroom cloud. The ad, being shown in 12 cities, recreates the ominous "Daisy" campaign commercial of 1964 that President Johnson used against Republican opponent Barry Goldwater.

In a lighter but perhaps equally eye-popping tactic, protesters in the organization Baring Witness said they might take their clothes off and march down San Francisco's Market Street.

They specialize in naked resistance, having disrobed in various remote locations and forming to spell "peace" and "no war" and to depict the peace symbol.

Organizers of the national rally invoked King, particularly his "Beyond Vietnam" speech of April 4, 1967, in the leadup to the long weekend marking the civil rights leader's birthday.

In that speech, King said the war convinced him he could not speak against the violence coming from the ghettos "without having first spoken clearly to the greatest purveyor of violence in the world today -- my own government."

The national rally begins at 11 a.m. EST on the National Mall in view of Congress. Protesters will march to the Washington Naval Yard and demand the United States give up its most destructive weapons. Participants were invited to dress as weapons inspectors, although the question of what an inspector looks like was left to their imagination.

Organizers pledged a peaceful march Saturday; for Sunday, members of the group United for Peace called for a rally and march to the White House featuring "nonviolent civil disobedience." They did not elaborate but suggested they were willing to get arrested.

Events will be policed by a force that has polished a kind of tough cop-charming cop routine, and has used flower power of its own.

In major demonstrations in the past few years, local authorities have strictly and swiftly confined protesters to approved areas, not hesitating to arrest those who cross the lines.

At the same time, they have talked early and often to protest leaders and made a show of chatting up demonstrators -- even giving them flowers before making a peaceful arrest.