A sudden and severe thunderstorm that swept through central Maryland and Northern Virginia yesterday resulted in the hospitalization of two men struck by lightning, a Montgomery County house fire, and a brief search and rescue of Prince George's County campers riding inner tubes on the Patapsco River.

A father and son in Howard County were struck by lightning as they worked to repair a tree damaged during a previous summer storm. Harold E. Sterner Sr. and his son, Harold Jr., were in stable condition last night at St. Agnes Hospital in Baltimore. They were not burned, but were being kept overnight for observation, hospital spokesmen said.

Lightning from the thunderstorms that were created when a cold front moving east from the Appalachian Mountains collided yesterday morning with the moist, warm air that has enveloped the Washington area for weeks, also was cited as the source of a fire that caused $100,000 in damage to a house at 15700 Bondy La. near Gaithersburg.

Ray Newcomb, a forecaster with the National Weather Service, said the severe thunderstorm watch in effect for most of Maryland yesterday would probably be lifted by early today as the cold air continued to make its way east. Newcomb said that although forecasters had issued warnings of the storms, many people were unprepared for the violent combination of rain, lightning and winds that in some places reached 35 miles per hour.

Yesterday's rescue effort on the Patapsco River, a popular fishing and rafting site, was a prime example. The search began after 13 youths attending a two-week day camp sponsored by the Maryland Capital Park and Planning Commission were caught in a sudden thunderstorm that hit the Baltimore region about 1 p.m., darkening skies and generating swift currents on the waste-deep river they were riding. Several campers, fearing the lightning cracking overhead, got out of the water shortly after beginning their ride.

Police and fire officials from Howard, Baltimore County and the state Department of Natural Resources arrived at the Daniels area of Patapsco State Park after receiving a call of a possible drowning. The call had been placed by a 14-year-old camper who became concerned after he lost sight of his friends who were traveling farther up the river. Two counselors who were awaiting the campers at the end of the two-mile ride also were worried when about six of their 13 charges were missing.

After less than half an hour, all the youths, age 12 to 15, had been found safe.

"We called weather this morning and there was a 50 percent chance" of thunderstorms, said Jan Steckle, one of the counselors accompanying the campers. "I guess we picked the wrong one."

Meanwhile, heavy rains during the weekend displaced three families from an Alexandria apartment building. According to Battalion Chief Jack Beam of the Alexandria Fire Department, a leaky roof at the apartment building at 3515 Mount Vernon Ave. caused the ceilings of three apartments to collapse, leaving the families temporarily homeless.

About 12,000 cable television subscribers in Alexandria were without service for much of Sunday after weekend storms snarled utility lines.Staff writers Virginia Mansfield, Marc Lacey and Laura Bischoff contributed to this report.