A week of November rainfall - sometimes barely a drizzle, but occasionally at torrential downpour - has brought an odd mixture of disaster and good fortune to Virginia, sending floodwaters through the southwestern part of the state and welcome relief to Northern Virginia's Occoquan Reservoir.

The rains, which continued for their seventh consecutive day yesterday, were forecast as liekly to linger on this morning in the Washington area and northern portions of Virginia, as D.C. and Virginia voters go to the polls.

The heaviest flooding occurred in Smyth and several other counties of southwestern Virginia, where an estimated 3 1/2 inches of rain were dumped on a number of small towns and rural communities over the weekend.

"We're evacuated approximately 300 people," investigator Jim Brickey, of the Smyth County sheriff's office, said yesterday afternoon. He was in Marion, one of the hardest hit towns. "A lot of the roads are washed completely out and a few houses were destroyed.

Yet, as Marion's drenched residents were starting to clear away mounds of mud dumped by the weekend deluge, the Fairfax County Board of Supervisors became the first Northern Virginia government to lift the nearly 2-month-old curbs on water use, imposed because of the diminishing water supply in the Occoquan Reservoir on the Fairfax-Prince William County border.

The Fairfax board's unanimous decision will take effect Wednesday. Prince William County and Alexandria are expected to follow suit today. The lifting of the water restrictions will allow Northern Virginia residents to wash their cars and will permit restaurants to serve water. The water restrictions, had also prohibited lawn watering, street washing, use of water-cooled air conditioners and the filling of swimming pools.

In the past week, more than 1 1/2 inches of rain fell in the Washington area, a heavy splash for the start of November. The average rainfall for the entire month of November has totaled just 2-9 inches during the last 30 years.

Charlie Chilton, a National Weather Service meteorologist, attributed the week of wetness to an unsual weather pattern. A low-pressure system became stalled over the southeastern part of the United States, picking up increasing moisture from the nearby Atlantic Ocean, he said. This unusually soggy mass, he added, then headed northward, leaving a blanket of rain wherever it went.

The damp air mass was further moistened, forecasters noted, by a tropical weather system that moved over from the Bermuda area and drifted off the Carolina coast.

In southwestern Virginia, numerous schools were reported closed yesterday because of the flooding and some were expected to remain shut today. Nearly 200 roads were reported closed in 13 counties. Barges broke loose from moorings on the New River, and at least one was reported to have crashed into a highway bridge.

Despite the weekend downpour and flooding, no drownings or other accidental deaths were reported in the region.

Although the rains prompted some initial fears that voting in some parts of Virginia might be disrupted, the flooding appeared to have had only one minor effect on balloting procedures. One voting precinct in Smyth County was shifted from a building east of the town of Atkins to another building in the town itself. The change in voting location was prompted by the flooding of a roadway.

In the Washington area, yesterday's rain apparently caused only a few minor incidents. The northbound lane of Rock Creek Parkway between Broad Branch Road and Joyce Street was closed during the morning rush hour because of flooding, a park service spokesman said.

The Virginia Electric and Power Co. reported a 40-minute interruption of electrical service for about 900 north Arlington customers. It was caused, a Vepco official said, after a tree limb fell on a power line. A Potomac Electric Power Co. spokesman said the weather caused a scattering of minor power disruptions.

For the Occoquan Reservoir, the November rains have meant billions of gallons of much-wanted water. The volume in the reservoir reached its lowest point ever on Oct. 26, dropping to just 1.85 billion gallons. By noon yesterday, according to Fairfax County Water Authority spokesman James A. Warfield Jr., the reservoir contained 5 billion gallons. It is expected to reach 6 billion gallons within two days.

When the Fairfax supervisors voted yesterday to lift curbs on water use, it was following a recommendation made by the water authority itself last Friday.

Ironically, as Warfield himself noted, the amount of water in the Occoquan yesterday morning was almost the same as the amount it held Aug. 5, when water restrictions were first set for Fairfax County. The change of season, however, apparently brought with it a change in outlook.

In August, Warfield said, Northern Virginia was facing two dry months, while now it is looking ahead to several wet ones. Northern Virginians also consume less water during fall and winter months. Warfield added.