Yesterday's rainstorm eased Northern Virginia's dwindling water supplies, but not without flooding Washington area roads, and causing accidents that included a massive three-mile traffic jam on I-95 at the Capital Beltway in Fairfax County.

The Occoquan Reservoir, which supplies drinking water to about 700,000 residents of Alexandria, eastern Prince William and Fairfax counties, had fallen to only 3.3 billion gallons from a normal level of 10 billion gallons before yesterday's rain, said Jim Warfield, spokesman for the Fairfax County Water Authority.

"We won't know until Monday, but if the watershed got similar rainfall to what they received [National Airport], it will go a long way toward eliminating the problem," Warfield said. The airport recorded 1 1/2 inches of rain. The rate of rainfall for the Washington area is running eight inches below normal for the year and the water authority has had to impose restrictions on water use because of the shortage.

More than two inches of rain had fallen at Dulles International Airport by 11 a.m. Saturday, almost half of which was recorded between 7 and 11 a.m., a spokesman there said. Virginia State Police Trooper Dale B. Johnson said the rain was partly responsible for a 9 a.m. accident that snarled northbound traffic for nearly three hours on I-95 after an 18-wheel, McLean Trucking Co. rig overturned on the ramp to the Capital Beltway.

The driver, Glenn Farrell Harper, 31, was charged with reckless driving.

Virginia Electric and Power Co. spokesman, Bill Bermilya, said that rain and winds that gusted to 31 miles per hour cut power to 2,100 homes in Arlington County, the Springfield area of Fairfax County, and Falls Church from 9 a.m. to noon. All but a few homes had power again by late Saturday afternoon, Vermilya said. Potomac Electric Power Co. officials also reported scattered power outages throughout its service area, but no major problems.

U.S. Park Police closed off Beach Drive, between Joyce and Broad Branch Roads because of flooding. Northern Virginia authorities reported several minor accidents and flooding on Woodburn Road near Gallows Road in Fairfax County. Route 110 and Marshall drive near Fort Myer, and the east end of Lee Highway in Rosslyn, were closed to traffic yesterday because of a foot of standing water, said Arlington police.

A coastal storm centered over southern New Jersey and the Delmarva Peninsula was responsible for the area's rain, said Frank Rosenstein of the National Weather Service. Washingtonians can expect a mostly sunny and cool, crisp Sunday, however, as the storm moves to the northeast, Rosenstein said.