Just as March began and it seemed that Washington might avoid winter's worst, a major storm slashed into the area last night, with thick snow falling and one of the heaviest accumulations in years expected.

By early today, snow depths ranged from two to six inches, with the storm's impact most severe on the area's southern edge. Forecasters expected a total of eight inches through much of the area by morning, and one prediction called for 12 or more inches before late tonight when the storm is expected to end.

"We're looking down the throat of a blizzard," said a meteorologist with Accu-Weather, a private forecasting service. High winds and blowing snow were expected to add today to the hazards of icy roads and slippery streets that began developing yesterday afternoon.

If as much as 12 inches of snow does fall, it would be the second heaviest accumulation here in at least six years, topped only by last year's once-in-a-lifetime mark of 18.7 inches, set Feb. 18 and 19.

By last night, the storm had already pushed the total snowfall here this season well above the 16.6-inch mark, which is average for a Washington winter.

Although snowplows and salt-spreaders were sent rumbling into action across the area, highway traffic was delayed, roads were lined with stalled and abandoned cars, and some streets were closed.

Snow emergency plans, which call for use of snow tires and chains, went into effect in most area jurisdictions.

Metro promised subways would run today, and Giant and Safeway food store officials said their stores will be open.

As the storm blanketed the area last night, authorities indicated that they were already thinking about Monday morning's rush hour but said it was too early for decisions.

A spokesman for the federal Office of Personnel Management, with jurisdiction over the schedules of 350,000 government workers here, said that if the heaviest snow ended by this afternoon and roads are cleared, employes should be able to go to work on schedule. But, he added, citing meteorological and other uncertainties, "it all depends . . . "

Area school officials indicated that no decisions on possible school closings would come before tonight.

Cliff Crowley of the National Weather Service said he would adhere to an earlier prediction of about eight to 12 inches by this evening.

However, Kevin Atchison of Accu-Weather said, "it looks like at least 12 inches," adding that he saw a "potential for up to 15."

Meanwhile, according to the National Weather Service, new snow accumulations last night ranged from about two to four inches in northern sections of Montgomery County, to about four to six inches in the extreme southern sections of Prince George's County.

Over the remainder of the metropolitan area about three to five inches of snow was reported. In some spots last night's snowfall added to accumulations that remained from Thursday's storm, giving an even greater total depth.

Washington's streets were littered with snow-stuck cars and trucks before dusk yesterday. All along Connecticut Avenue from Dupont Circle to Chevy Chase, stalled cars caused blocks-long traffic jams. Where cars could move, it was a snail's pace.

Eight vehicles including a Metrobus collided in a chain-reaction accident at Division and Burroughs avenues NE. Firefighters untangled another eight-car pileup on 16th Street near Walter Reed Hospital.

A car-strewn stretch of Suitland Parkway between Stanton Road and Alabama Avenue was described as "a parking lot," and police were forced to close the steep section of 15th Street NW near Meridian Hill Park.

Across the Potomac, in Alexandria, police reported that cars on Shirley Highway were starting and stopping every few feet because of innumerable fender-benders. Similar traffic problems were reported throughout the Virginia and Maryland suburbs.

National Airport closed from 8:10 to 9:13 p.m. to permit plowing of its main runway, and officials said they expected to resume plowing about 2 a.m. and reopen at 7 a.m. today.

During the time National was closed, one plane scheduled to land there was diverted to Dulles, according to a spokesman for the Federal Aviation Administration, which runs both airports. He said Dulles remained open all day.

A spokeswoman for Greyhound bus lines said service was halted last night between Washington and such points south as Roanoke and Winston-Salem, N.C.

The storm was reported heaviest in southern areas, weakest in areas north of Washington. At a time when seven inches of snow was reported in Roanoke, only one inch was reported in Baltimore.

Greyhound said bus service to points north and west of Washington was delayed last night from one to two hours.

Metro buses "were and still are up to an hour late," said Metro spokesman Cody Pfanstiehl.

However, he said subway trains were running on schedule. Empty trains would be run over exposed tracks all morning, to keep them clear, he added.

According to the forecasters, the snow should stop by tonight and temperatures should moderate by Tuesday. Below freezing marks were recorded all day yesterday, with lows of 8 degrees expected overnight.

Although the low temperatures moved into the area from central Canada last Wednesday, it was not until early yesterday morning that weather forecasters knew for certain that a blizzard was on the way.

Snow blanketed the East Coast as far sourth as North Carolina, as far north as Pittsburgh and as far west as Louisville by late afternoon. Dense cloud coverings, rain and sleet extended as far south as Miami.

Meteorologists said the storm resulted from warm, moist air moving up from the Gulf of Mexico and overruning the cold, dry air that, in the last week, has flowed south across the Canadian border.

"What is happening is that we're getting a lot of this moist air on top of the cold area and it forms snow and drops right on down through the clouds," said an official at the National Weather Service.

The ferocious snowfall in Washington caused confusion and concern for pedestrians as well as drivers.

In the lobby of a downtown Washington office building, a small girl who had accompanied her father to work pointed at a picture window, across which swept an endless array of wind-driven snowflakes, and said, "I don't want to go out there."

At a supermarket in Prince George's County, a horde of customers, apparently remembering the crippling snowstorm of a year ago, swarmed through the aisles and all but bought out the store. "It's the busiest that I have ever seen," the store manager said.

Although it is a Washington tradition that snow strikes fear and terror into the hearts of local residents, exceptions to the rule can always be found.

"I think it's beautiful," said Suzanne Lamar, as she waited for a bus on 16th Street in the District. Apparently mindful, however, that there are at least two sides to every issue, she added: "It'll be nice when it clears up."