A gray, dismal and almost sunless week ended here yesterday with an unexpectedly heavy snowstorm that brought many sections of the Washington area their greatest snow accumulations of the winter.

By late last night snow was measured at three inches at National Airport -- the most there this winter. Three inches were also recorded at Dulles International Airport.

Unofficial reports from some parts of suburban Maryland indicated accumulations of as much as five inches.

Throughout the area, the snowfall was much more than expected. In the morning, forecasts called for no accumulation, and as late as 4 p.m. the prediction was for an inch or less.

Highway officials said they were caught short and forced to mobilize their fleets of salt and sand trucks on an emergency basis.

"Everybody said it was going to be a light snow, but right now we are going full blast and bringing in everything," said Dick Robson of the Virginia Department of Highways and Transportation.

Relatively light traffic yesterday afternoon and evening appeared to save the area from the paralyzing tie-ups frequently experienced here with snow, although many minor accidents were reported as roads appeared to become slippery, slushy and in spots snow covered.

"Most of the streets in Fairfax are covered with snow and slush and vehicles are sliding off into ditches," Lt. Dana Libby of the Fairfax County police department said last night.

"We are not keeping count of the noninjury accidents because there are so many," he said.

As the swirling snow filled the afternoon skies, visibility was cut to little more than a half-mile in places. Airplanes taking off from National Airport vanished from view almost immediately. The airport was closed for about a half-hour to permit plowing of runways.

At first, with temperatures a few degrees above freezing, the wet, fast-falling snow melted as it reached streets and sidewalks. But after two or three hours, it began accumulating there, giving pedestrians a rare opportunity to leave deep footprints in the nation's capital.

In the District, George Schoene of the city's transportation department said, "We are salting the main streets as fast as we can."

Although Schoene expressed the hope that today's temperatures -- expected to rise into the 40s -- would melt ice and snow, the prospect of freezing temperatures overnight raised the possibility of hazardous driving conditions this morning.

By late last night, National Weather Service forecaster Bob Oszjaca said enough snow had blanketed the area to make it unlikely that one day of 40-degree temperatures could melt it all.

Snow began falling in the area in midafternoon. By 7 p.m. accumulations had reached three inches.

After that, the intensity of the snowfall began abating. By 1 a.m. today the snow had stopped.

The three-inch accumulation is about an inch more than was recorded at the official measuring station at National Airport during the heaviest previous storm this winter, which occurred Feb. 10 and Feb. 11.

The snow was brought by the fourth winter storm here this month. The first brought sleet and freezing rain on the morning of Feb. 7 and created a morning rush-hour traffic catastrophe.

Another snowfall on Feb. 14 dumped about one inch of snow at National Airport.

Even without the periodic storms, this month has been, for the most part, gray and dismal. Weather service figures show that there have been only three sunny days since Feb. 8. Many of the days have been cold and drizzly, and sometimes foggy. Sunshine is expected this afternoon.

Tonight's temperatures are expected to be below freezing, and tomorrow's highs will reach the 40s again.

In explaining how the snowfall took forecasters by surprise, the weather service's Oszjaca pointed to the unexpected interaction among three weather systems.

One was a high pressure system in New England, the others a pair of low pressure systems in western Virginia and in western North Carolina, he said.

At first it was expected that the New England high and the North Carolina low would dominate the meteorological scene and would create a rather feeble storm, particularly in this area.

As the storm was brewing, however, the unexpectedly vigorous intervention of the low pressure system in Virginia, of which relatively little had been expected, pulled the storm toward Washington.