A U.S. State Department employee was critically injured yesterday when he was struck by lightning near the Lincoln Memorial as thunderstorms rolled through the Washington area, triggering several house fires, flash flooding and power outages for thousands.

The 39-year-old man, whose name was not released, was struck underneath a tree, where he had run in the mistaken belief that trees offer protection, said Alan Etter, a spokesman for D.C. Fire and Emergency Medical Services.

The lightning hit the man in the stomach shortly after 5:30 p.m. and exited through his right foot, briefly knocking him unconscious, Etter said. An off-duty U.S. Secret Service agent ran to the man and administered mouth-to-mouth resuscitation, helping him regain consciousness, Etter said.

The man was transported by ambulance to George Washington University Hospital in critical but stable condition, Etter said.

In the District, firefighters rescued two motorists who were stranded in 18-inch-deep water on South Capitol Street near Interstate 295. In Prince George's County, firefighters pulled a motorist from his van on the flooded Suitland Parkway in Forestville.

The late-spring storms arrived in midafternoon on a hot, oppressively muggy day and continued into the evening, dropping as much as an inch of rain an hour in some areas and causing flash flooding in Northern Virginia, the District and Maryland, said Calvin Meadows, a meteorological technician with the National Weather Service.

In Prince George's, lightning apparently triggered fires at homes in Bowie, Hyattsville and Brandywine. An apartment building on Lorring Drive in District Heights also caught fire, said Capt. Chauncey Bowers of the Prince George's County Fire/EMS Department. No injuries were reported in any of the fires.

Bowers said the storms knocked out six of seven communication channels for the county fire department for several hours, but that firefighters were able to manage.

In the Charles County town of La Plata, which was hammered by a deadly tornado two years ago, an ominous black thundercloud swept through about 7 p.m., triggering a warning siren and a voice on a loudspeaker that repeatedly warned: "Do not delay."

It was pizza night at Casey Jones, a restaurant in the center of town, and customers had filled the restaurant and outdoor patio when the storm came through. When the siren blared, customers on the patio rushed inside, leaving their food on the tables. The kitchen had to re-cook several meals.

"It came very quickly; it was very rainy and windy. It was very intense for about 15 minutes," said waitress Jen Cox, 29, of La Plata. "Then it was over." Cox said that since the 2002 tornado, residents are extremely cautious anytime a tornado warning is issued.

"The sensitivity level here is very high," she said.

In St. Mary's County, authorities said there was flooding in low-lying areas near Lexington Park. About 650 customers throughout Southern Maryland lost power, the Southern Maryland Electric Cooperative said.

In Northern Virginia, about 2,300 customers were without power as of 10:30 p.m., according to Dominion Virginia Power's Web site. Pepco reported 3,000 outages in Prince George's, 138 in Montgomery County and 2,600 in the District. Power was restored earlier in the evening to thousands of other customers in that area, said Robert A. Dobkin, a Pepco spokesman.