Dozens of brush fires, fueled by high winds and unusually dry woods and grasses, scorched more than 150 acres in Northern Virginia during the weekend, fire officials said yesterday.

Smaller brush fires broke out in wooded areas of the District near Fletcher's Boat House, 4940 Canal Rd. NW, and in isolated sections of suburban Maryland, they said.

Most of the brush fires were concentrated in Fairfax and Loudoun counties, fire officials said, while others were reported in Montgomery and Frederick counties in Maryland and in Prince William, Washington, Frederick and Fauquier counties in Virginia, said Loudoun County Fire Board dispatcher John Kaviness.

Loudoun County fire officials said one firefighter died Saturday while battling a three-alarm brush fire in the Philomont area. They said Frederick Le Grys, a 25-year member of the force, collapsed about 4:30 p.m. and was taken to Loudoun Hospital where he was pronounced dead. The cause of his death had not been determined.

"This has been some of the worst I've seen," said Stanley Lee, chief of the Philomont Volunteer Fire Department. "We need some rain. The ground's dry."

Kaviness said the fires apparently started as a smattering of small brush fires Saturday near Lovettsville in northwest Loudoun County. By Saturday afternoon, about 20 fires were reported in rural Loudoun County alone, he said. Some of the larger blazes, Kaviness said, required as many as 50 firefighters.

Fairfax County fire officials said they fought at least two major brush fires yesterday that took several hours to extinguish and claimed nearly 100 acres.

Fire department spokeswoman Pam Weiger said a blaze reported about 2 p.m. in a wooded area near the 9100 block of Ox Road in Lorton, Va., burned for nearly five hours, before it was extinguished.

An earlier fire on Stull Road in Centreville, Va., took about three hours to bring under control. Weiger said no injuries or property damage were reported in the fires.

Kenneth Wells of the Fairfax Fire Department said similar fires were fought Saturday in Herndon and in residential Great Falls where 50 acres were scorched.

Because of the number and intensity of the brush fires, area fire officials said they were unable to report how many firefighters and pieces of equipment were used.

Throughout much of the weekend, firefighters used helicopters to find the hot spots and then used four-wheel-drive jeeps and other vehicles to reach the fires, some fanned by winds gusting to 23 mph.

"When the wind is blowing the fire spreads fast," Wells said.

Loudoun County's state forest warden, Landon Compher, said brush fires are not uncommon for this time of year. In Florida, more than 211,635 acres of forest and grasslands have been destroyed by brush fire in 1985.

Locally, the fires have been particularly harsh in Northern Virginia because of recent weeks of dry, warm days, Compher said. Last year, rains helped to prevent fires during the brush fire season -- March 1 through April 15.

Compher cited carelessness as the primary cause of the fires. Some have been linked to motorists tossing smoldering cigarette butts from cars.

In Virginia, it is against the law to build a fire outside during the brush fire season without a permit, authorities said. In Fairfax County, as in the District and Maryland, it is unlawful to build a fire outside at any time without special permission.

Meanwhile, two firefighters were treated for minor injuries suffered while fighting a large brush fire yesterday in a state park in Boonsboro, Md., near Frederick County, according to a fire official.

Fire officials said the fires probably won't end before it rains. Forecasters said there is a 30 percent chance of rain today.