WASHINGTON (Reuters) — The U.S. government ordered a partial shutdown Monday in the face of anti-globalization protests, and demonstrators planned to gather before dawn to prevent world financial leaders from meeting.

Both sides' plans reflected clashes Sunday in which police with batons and pepper spray beat back protesters out to block financial leaders from the world's richest nations.

In a rare move, the federal government announced late Sunday that only emergency workers should report to work Monday in a large area surrounding the International Monetary Fund and the World Bank, where thousands of protesters were expected to target world financial meetings again.

One of the protest organizers said mobilization would begin in the predawn hours Monday in a bid to keep financial officials from gaining access to fund and bank buildings.

The Office of Personnel Management said nonessential federal workers at the State, Treasury, Commerce and Interior departments, the White House, and other key agencies would have an unexpected day off at the recommendation of federal and local law-enforcement officials.

Washington Police Chief Charles Ramsey forecast bad traffic during Monday's morning rush hour as protesters tried to block the sixth and final day of meetings at the IMF and World Bank.

"I think that people can just about bank on having traffic congestion like they have not seen here," Ramsey said.

Anti-globalization protesters, who say the institutions' policies hurt the poor and destroy the environment, tried to block financial leaders from meeting Sunday but shut out only a few finance ministers.

"Despite the scare tactics, the threats, the harassment, the surveillance, the helicopters overhead, the raid of our workshop space and our teaching area, their tear gas ... and pepper spray, we will not be silenced," Nadine Bloch of the Mobilization for Global Justice told a news conference.

Police arrested 20 protesters Sunday, bringing to 657 the number of people they say have been detained in the last two days of protests. Organizers say 900 were arrested, with 300 still in jail. During a week of similar protests in Seattle last December, 525 people were arrested.

Protest organizers said they had 20,000 demonstrators on the streets of the capital Sunday. Police estimated that 10,000 protesters attended one demonstration on the grassy Ellipse near the White House, a good-humored rally that drew people whose causes ranged from the battle against AIDS to Third World rights.

Despite the protests, the Group of 10 industrialized countries and a key IMF panel met on time, discussing reforms to make sure that the problems that caused the financial meltdown of 1997-99 did not occur again.

As in the anti-trade protests in Seattle last year, the demonstrators in Washington underwent weeks of training and appeared to be highly organized. But unlike Seattle police, those in Washington responded quickly to attempts by protesters to disrupt the meetings here, keeping the crowds mostly under control.

Police beat protesters with batons, fired pepper spray and rode their motorcycles into the crowd to try to break up demonstrations just blocks from the White House.

In what seemed to be an isolated incident, police appeared to use tear gas after skirmishing for several hours with the demonstrators, many of whom wore bandannas and masks. The use of force calmed the volatile situation.

A police spokesman said an investigation had been launched into whether police had actually used tear gas on the protesters, a move that he said only two top police commanders could authorize.

Washington Mayor Anthony Williams defended the police action and vowed to prevent a repeat of events in Seattle, where there was widespread damage to property.

Monday's partial shutdown, rarely used except for weather-related emergencies, affects a large area bounded by 12th Street N.W., 23rd Street N.W., Constitution Avenue and K Street N.W., the Office of Personnel Management said.

Outside that area, government agencies would operate, but workers could take unscheduled leave.

"This is obviously a decision that we don't take lightly. It's very unusual and very rare," a spokesman said.

The last time federal workers stayed home, aside from some snow days this winter, was during last year's NATO summit in Washington, when officials also cited security concerns.

District of Columbia government workers will also be allowed to take unscheduled leave and stay home Monday.

Protesters believe IMF and World Bank policies serve the interests of rich countries at the expense of the world's poorest people, a criticism shared by some economists and members of Congress.

IMF meetings went ahead Sunday as busloads of delegates were able to enter through a secure entrance, many arriving at dawn, before the crowds gathered.

But protesters hoped to beat them to the punch Monday, one organizer said, with activists due to begin arriving at 3 a.m. EDT.