The long dark winter of 1978 grew longer and darker yesterday as another substantial snowfall - the 10th of this unusual Washington winter - created a now familiar mix of majesty and slush.

By late yesterday, 3 inches of new snow had fallen at National Airport, the National Weather Service official observation point here. That brings the March total to 7.9 inches and the total for the season to 22.6 inches.

Temperatures hovered just below freezing most of the day, icing roads and generating a multitude of fender-bender accidents.

Late yesterday morning at the height of the snowfall, a reporter counted 13 auto accidents on Shirley Highway between the 14th Street Bridge and the Capital Beltway in suburban Virginia.

Fairfax County police reported 175 accidents between 7 a.m. and 3:15 p.m. throughout the county, including at least two involving serious injuries. In one, on Georgetown Pike near McLean, Stanley R. Repass, 27, of Rockville, was pinned under a Jeep. He was reported in critical condition at Fairfax Hospital. In the other, on Telegraph Road near Alexandria, Thelma T. Hatten, 43, of Alexandria, lost control of her car and slid 200 feet into a power stanchion. She was listed in critical condition at Alexandria Hospital.

Maryland State Police also reported numerous accidents on the Beltway, Interstate 95 and Route 50. A tractor trailer rig overturned on Route 50, injuring its driver, police said.

A Montgomery County fire truck went out of control and struck a utility pole on Wayne Avenue near Dale Drive, fire officials said. Its driver suffered minor injuries but returned to work, one official said.

An accident involving a U.S. Park Police cruiser stalled home-going commuter traffic on the George Washington Memorial Parkway in Virginia for more than an hour last night. A police dispatcher said there was "heavy property damage" to at least two vehicles, but no injuries.

Schools closed early in Fairfax and Prince George's counties and in Falls Church, and public bus service was slowed in some areas, especially during the ice-impeded afternoon rush hour.

The snow gradully tapered off late in the day and began turning to sleet and rain last night. Weather service forecasters called for warming temperatures and more rain today.

For many, this has been an unending winter, a winter of gloomy days and long cold nights. There is a ragged, weary look about things. Sootstained snow has been piled by roadsides for weeks. Street are pockmarked with potholes.

Crocuses and other early spring flowers, which often bloom in February, have not shown their heads. School children, surfeited with sledding and skating, even are complaining about the frequent closing of school. Exam schedules have been disrupted. Lost days will have to be made up in the spring when it will be warm and pleasant.

Weather service statics confirm the impression that it has been a bad winter. Snow, rain, heavy cloudiness and frigid temperatures have prevailed. Snow has fallen 23 of the 67 days so far this year. February averaged 31.4 degrees - 5.6 degrees below normal - the coldest February since 1963. The normal maximum daytime temperatures for this time of March is 52 degrees but the thermometer has not been above the 30's since mid-February.

Though no snowfall records have been set so far this winter, a series of 10 relatively small but evenly distributed storms has left snow on the ground in shaded areas almost continuously since early January - an unusual phenomenon for the Washington area.

Why the weird winter?

The central Atlantic Coast including the Washington area has become a "battle zone" of two colliding wind systems, the polar jet stream and the subtropical jet stream, says J. Murray Mitchell Jr., senior research climatologist for the National Oceanic and Atmospheric Administration.

A stationary ridge or ripple of the high altitude polar jet stream has been pulling cold Canadian air in a southeasterly direction down into the Washington area almost continuously since early winter, Mitchell said. At the same time, the subtropical jet stream, which normally flows across the southern tier of American states, has been shooting warmer air toward Washington in a northeasterly direction, putting it on a collision course with the polar winds, he said.

"The two systems are fighting each other," Mitchell said, "and we're caught in the middle." The collision has caused the unsettled and stormy weather of the winter, he said, but because Washington has been "more on the polar side of the battle," the weather here has remained consistently cold with none of the mid-winter thaws that occur in more typical years.