The death toll in Sunday's severe thunderstorm was raised yesterday to at least three following reports of a motorcycle accident in Prince William County.

Earl Smith, 29, of Manassas was killed when a tree uprooted by the storm's high winds -- clocked at more than 60 miles an hour -- struck his motorcycle on Grant Street, across from the Prince William County courthouse.

Manassas police found the victim about 4:30 p.m. still mounted on his motorcycle, which was held upright by heavy limbs of the fallen tree. Repeated attempts to revive Smith failed, authorities said.

Two other deaths were reported immediately after the storm struck here Sunday. An Air Force colonel was killed at Fort McNair in Southwest when he was struck by a limb torn from a tree by the high winds.

Another man was drowned after his sailboat capsized in the Potomac River south of the Woodrow Wilson bridge. Three other persons on the boat were rescued by the Coast Guard.

In addition, two persons died in Howard County, Md., in a boating accident that apparently occurred just before effects of the storm were widely observed in the Washington area.

Police said Brian Oliver Monteith, 5 of Lanham and Gregory Yingling, 31, of Laurel, died after their 12-foot boat capsized in the Rocky Gorge reservoir.