While President Bush's supporters celebrate his inauguration today, thousands of protesters across the United States aim to hit the streets with demonstrations and rallies against the returning administration.

"There are some in this country who are just not in the mood to let the president have his day in the sun," said James Hudnut-Beumler, dean of Vanderbilt University's Divinity School and an expert in protest movements.

Although Mr. Bush was met with protesters when he was sworn in 2001, inaugural protests are rare historically, Mr. Hudnut-Beumler said.

"Presidents are usually given an opportunity in their inauguration address to try to claim the affections and interests of the whole nation, including people who didn't vote for him."

But in San Francisco, Los Angeles and Seattle, organizers expect thousands of demonstrators to gather today for speeches and rallies. In dozens of smaller communities -- from Bridgewater, Mass., to Flagstaff, Ariz., -- rallies, marches and demonstrations also are planned. Former Democratic presidential nominee George McGovern is the featured speaker at a demonstration planned in Santa Cruz, Calif.

For some demonstrators, the reasons to protest are simple.

"We're objecting to Bush being reinstalled as president of the United States. He's illegitimate," said Carol Brouillet of Palo Alto, Calif., who plans to spend today in downtown San Francisco displaying huge panels of photographs of troops killed in Iraq. Miss Brouillet, who said she thinks Mr. Bush used the terror attacks of September 11, 2001, as a pretext for war, has shown the photos at various demonstrations.

Others said they were seeking comfort in numbers.

"We don't feel that Bush's supposed mandate represents us. Maybe this is just therapy for us for feeling helpless and hapless," said veterinarian Dr. Paul Makidon of Ann Arbor, Mich.

In addition to street protests, some anti-Bush groups are calling for a daylong economic boycott, pressing critics to stay home from work and not spend any money.

"We've tried marching in the streets to stop the war; we tried writing letters; we tried initiatives on the Web, but Bush doesn't listen. It seems to us the only thing Bush and the Republicans will listen to is money," said David Livingstone of Detroit.

Tim Castleman, a Web site designer from Sacramento, Calif., began his protest almost a week before the inauguration, boarding an eastbound Amtrak train that he dubbed the "Peace Train" to head for the District. He calls for increased rail and public transit funding and relates this demand to the war in Iraq.

"A person traveling by train," he said, "will consume half as much as a person on an airplane, with a corresponding reduction of pollution and funding of wars for oil."

His protest is to get Mr. Bush and Congress to "lead us out of our wasteful path," he said.

Police in many communities said they are prepared for the outcry and have been working with protest organizers on march routes and other plans.