Balmy temperatures finally gave way to winter early yesterday as a mass of arctic air blew into the Washington area just before dawn, knocking down tree limbs and power lines and sending many of the area's homeless into shelters.

With the wind gusting at more than 40 miles an hour, midday temperatures had the chilly feel of the high teens, compared with Sunday's record-tying high of 71 degrees.

At noon yesterday, the temperature at National registered 40 degrees, a mark forecasters say the area won't climb to again until at least Friday.

"This is definitely the coldest weather we have seen this winter season," said forecaster Richard Hitchens, who said the season's previous low reading at National was 29 degrees. Overnight lows were expected to be 15 to 20 degrees, and the temperature today is expected to climb no further than the thirties under clear, sunny skies.

Temperatures are forecast to warm slowly in the next three days, with a high of about 40 predicted for Friday.

Normal high temperatures for this time of year are in the mid-forties.

Yesterday's blast of cold, propelled into the area by the meandering jet stream, is the remnant of the arctic mass that has shocked the West Coast and Central Plains with subzero readings and major snowstorms for the past week.

However, Hitchens said, the cold front has warmed during its trip east, ushering in crisp, clear weather here and eliminating any hope of a white Christmas. Snow flurries were reported yesterday in West Virginia and Western Maryland, where an inch of snow was reported in Frostburg.

The change from unseasonably warm to unseasonably cold weather began yesterday at precisely 5:59 a.m., when weather monitors at National Airport recorded an abrupt shift in the winds to the northwest. By 7 a.m., the temperature had dropped 16 degrees from its 5 a.m. reading of 65.

The brisk winds played havoc with tree limbs and power lines, disrupting electrical service during the day for several thousand customers and ending a scheduled holiday for electrical repair crews and tree contractors.

Nancy Moses, spokeswoman for Potomac Electric Power Co., said service to about 1,500 customers scattered across the area was knocked out by winds during the morning.

Moses said that the early power failures were caused primarily by falling limbs that knocked down power lines along neighborhood streets. The service interruptions were in Northwest and Northeast Washington, Fort Washington, Oxon Hill, Upper Marlboro, Rockville, Silver Spring, Potomac and Bethesda.

Most of the downed lines were repaired within hours, and all service was restored by last night, Moses said.

A spokesman for Virginia Power Co. said no more than 100 customers lost electricity yesterday because of the strong winds and cold weather.

As evening fell, a steady stream of homeless people made their way into area shelters.

Chuck C. Ugoji, a social service representative with the city's hypothermia crisis intervention unit, said last night that District shelters were filling up more rapidly than usual and that many were at or near capacity.

Barbara Burke-Tatum, the District's social services commissioner, said yesterday that city workers would be out overnight trying to urge homeless people sleeping outside to go to a shelter.

If all shelters were filled, she said, the city would house homeless men in the Wheatley Recreation Center, in the 1200 block of Morse Street NE, and homeless women in the lobby of the Department of Employment Services building downtown.

But last night Ugoji said it didn't appear that it would be necessary to open the overflow shelters.