Electricity was knocked out to thousands of residents of the District and Maryland early yesterday when a ferocious, fast-moving storm blew through the area, bringing down power lines, toppling trees and awakening many people.

More than 18,000 Pepco customers were without lights and air conditioning late last night. In some cases, residents said the utility company told them that their power would not be restored until today or tomorrow, which the National Weather Service predicts will be the start of several days with temperatures in the mid- to upper 90s.

The storm punched its way through the region, leaving severe damage in some pockets, particularly sections of Silver Spring, College Park, Oxon Hill and the District east of 16th Street NW. In the 400 block of Columbia Road NW, a towering pecan tree crashed through Benjamin Richardson's roof. Other areas experienced little or none of the storm.

Richardson was in bed when a lightning strike lighted up his room just after 2:30 a.m.

"Then it struck again real loud, and I decided to get up and go to the bathroom to look out the windows," he said. Minutes later, his roof collapsed and the tree landed on his bed.

Richardson, who rushed out of his house, said the second floor was destroyed. But he did not lose power or air conditioning in the rest of the house.

Others did, including D.C. Council member Adrian M. Fenty (D-Ward 4), who said he had received numerous calls from constituents without power.

The number of outages peaked yesterday morning with 52,000 of Pepco's roughly 725,000 customers without power, said Robert Dobkin, a spokesman for Pepco.

He said that most customers would have their power back by tonight but that it would take until tomorrow morning to restore power to everyone.

Pepco said storm damage was concentrated along the Georgia Avenue corridor from southern Montgomery County through the District and into Prince George's County. More than 10,000 homes remained without power in the District shortly after 10 p.m. For Montgomery, the figure was 6,500, and for Prince George's, almost 2,000.

The D.C. Department of Transportation received more than 100 calls about damage caused by trees as well as reports of malfunctioning traffic signals at about 20 intersections across the city, spokesman Bill Rice said. The National Weather Service received reports of 200 trees down in the District.

"It's probably the strongest thunderstorm we've had in the D.C. area this summer," said James Brotherton, a meteorologist with the Weather Service in Sterling. "What happened is typical, but the way it came together is pretty sudden."

Meteorologists issued severe thunderstorm warnings before heavy rain came, along with lightning and wind gusts of about 60 mph.

Brotherton said a weak cold front from Pennsylvania slammed into moist air and triggered the storm. He said bad weather popped up about midnight east of Frederick along Interstate 70.

Samuel Compton said lightning hit a tree next to his house in the 6600 block of Third Street NW about 2:30 a.m., then a power line ignited his Lincoln.

When the fire department came, he said, "it was blazing."

Compton, 82, said he had just filled it with gas and "the firefighters were afraid it was going to explode."

But the storm was nothing like 2003's Hurricane Isabel, said National Weather Service forecaster Rich Hitchens.

"This was just a thunderstorm," he said.

Staff writers Michael Laris, Martin Weil and Avis Thomas-Lester contributed to this report.

Trees and branches lie across houses and utility wires along Brunett Avenue in Silver Spring.