Downtown Washington will be a busy and eclectically populated piece of American turf this weekend, with protesters, counter-protesters, international bankers, bookworms, baseball fans and enthusiasts of the odd-looking, two-wheeled human transporters known as Segways descending on the nation's capital.

In addition to today's antiwar rally, march and concert near the White House and Washington Monument, expected to draw about 100,000 people, the Mall will be the site of the National Book Festival sponsored by the Library of Congress every year.

Nearby, the World Bank and International Monetary Fund will hold their fall meetings, and in the Hotel Washington, SegwayFest will draw dozens of the gyroscopic devices and their proud owners for a national convention. At Robert F. Kennedy Memorial Stadium, the Washington Nationals will play the New York Mets tonight and tomorrow afternoon.

Transportation officials are asking people to leave their cars at home and take Metro. Police will be closing many downtown streets at various times and mobilizing their forces for a busy weekend.

"We are expecting a very large crowd for the antiwar demonstration," said D.C. Police Chief Charles H. Ramsey, adding that he thinks the number of protesters could "easily exceed" the 100,000 estimated by organizers.

D.C. police yesterday activated 14 closed-circuit surveillance cameras to help them monitor the antiwar demonstrations and any activity near the IMF and World Bank. The cameras send live video feeds to a command center at police headquarters.

Ramsey said he has canceled days off for officers and put them on 12-hour shifts to boost staffing for today's demonstrations and to sustain patrols in the city's seven police districts. He said several hundred officers will be deployed downtown to monitor the march, rallies and counter-protests.

"We don't anticipate any problems," Ramsey said. "We'll monitor the march as it proceeds through downtown, but we don't anticipate any problems as a result of the parade."

Ramsey said police will pay attention to the possibility of protests at the World Bank and IMF, though a rally targeting those institutions is planned several blocks away at Dupont Circle. "We'll have to wait and see how that goes," he said.

U.S. Park Police, who patrol the Ellipse and other areas where rallies are being staged, also have canceled days off. They will have several hundred officers in uniform, in plainclothes, on horseback and on bicycles patrolling the crowds, said Sgt. Scott Fear, a Park Police spokesman.

The security detail will include the area around the National Book Festival, which will be on the Mall between Seventh and 14th streets.

Book festival spokeswoman Audrey Fischer said organizers of the fifth annual event, which will be held from 10 a.m. to 5 p.m. today and is free and open to the public, are working with Park Police to ensure that there is appropriate crowd control in light of other events on the Mall.

First lady Laura Bush, who hosts the event each year, will have a breakfast for the featured authors at the White House this morning, but organizers are unsure whether she will make an appearance at the festival, Fischer said.

In addition to the introduction of poets, mystery authors and children's storytellers, the book festival will include the launch of a "book relief effort" to restock libraries destroyed by Hurricane Katrina and provide books to the children affected by the storm. It will also be host of the Veterans History Project, a grass-roots effort to document the stories of veterans from World War I through current conflicts and those who supported war efforts on the home front, according to the Library of Congress.

Park Police will also ensure that monuments and tours remain open and accessible to tourists who want to take in more traditional sites this weekend, Fear said.

Transportation officials are not anticipating any major problems. A Metro spokesman said the system will not run extra trains but will have additional personnel at downtown stops to help visitors.

"People in this area are pretty darn good at this stuff and these events. We just have to remember what to do," said D.C. Transportation Director Dan Tangherlini. "Obviously, we're encouraging people to take Metro this weekend."

Many of those coming into town for the demonstrations will be arriving by charter bus. Bus drivers have been asked to drop their passengers on Pennsylvania Avenue NW between 13th and 14th streets, south of Freedom Plaza. The buses will park at various suburban Metro stations and pick up their passengers there after the rally, according to protest organizers.

Organizers say the flow of pedestrian traffic around the Mall should be good, noting that there will be no police security checkpoints.

Police are closing streets around the IMF and World Bank at 18th and H streets NW, the area around Constitution Hall and streets near the antiwar march route.

The antiwar rally is scheduled to begin at 11 a.m. at the Ellipse. The march will start about 12:30 p.m., and a concert is scheduled at the Washington Monument grounds from 3 p.m. until 1 a.m. Counter-demonstrators plan to be along the parade route and at the U.S. Navy Memorial at Seventh Street and Pennsylvania Avenue NW today.

Tomorrow, a coalition of conservative groups is sponsoring a rally in support of the Iraq war at noon on the Mall at Fourth Street NW.

Staff writer Del Quentin Wilber contributed to this report.

Pedro Alverez, left, and Brian Ralda, workers with Classic Tents, set up a tent for the antiwar rally. A concert and march are scheduled.Employees of the party company It's My Party set up for this weekend's antiwar rally and concert. Police say attendance could exceed 100,000.