A narrow band of thunderstorms whipped swiftly across the Washington area yesterday, bringing bursts of rain, flashes of lightning and violent gusts of wind that knocked out power to 25,000 homes and businesses.

At Dulles Airport, where a 94-mile-an-hour gust, well above hurrican force, was clocked at the control tower a 100-foot section of roof was torn from a cargo storage bay. In nearby Chantilly, part of a roof was ripped off Brookfield Elementary School, sending clumps of insulation flying across nearby lawns.

Within a few minutes around 4 p.m. yesterday, skies grew black with clouds, winds rose, temperatures plummeted from the 90s to the 70s, and rain fell in sudden, fierce torrents. Half and inch was measured in Bowie in one 10-minute period.

Yippies and other political dissidents, who had been convening south of the Reflecting Pool through the hot, hazy early afternoon, bolted along with regular tourists for the shelter of the Lincoln Memorial when the rain began to fall.

The unplanned encounter between the Yippies and the conventional tourists, united in their desire to escape the elements, was brief and caused no problem, according to the U.S. Park Police.

Although the storms capsized sailboats in the Potomac River and toppled many trees, including some that fell across roads, temporarily typing up traffic, there were no immediate reports of serious injury.

Most of the damage to power lines apparently occurred in the area served by the Potomac Electric Power Co. -- the District and Montogomery and Prince George's counties.

About 20,000 homes and businesses in these areas lost power at some point, according to a spokeswoman for Pepco.

By late last night, she said, power had been restored to all but about 2,100. Particularly hard hit, she said, were the Upper Marlboro and Cheverly sections of Prince George's County and the Gaithersburg and Silver Spring areas of Montgomery County.

In Virginia, where about 5,000 homes and businesses were cut off at the peak, service to all but 500 had been restored within a few hours after the storm, according to the Virginia Electric and Power Co.

Heaviest wind and lightning damage to power lines was reported in Fairfax County, Leesburg and Fredericksburg.

The storms, part of a line that swept eastward over much of Virginia, reached a peak near Dulles. Besides the 94 mile-an-hour gust measured at the 14 story-high control tower, a 78 mile-an-hour gust was recorded at ground level.

Golf ball-sized hailstones were reported in Chantilly, the Fairfax County area about three miles south of the airport, where part of the roof was torn from the Brookfield Elementary School, 4200 Lee's Corner Road.

"It looks like the roof peeled off and opened up like you'd peel off the top of a can," said one witness.