A freak early autumn snow storm pounced on Washington yesterday, smothering some areas in up to four inches of snow, snarling commuter traffic, snapping tree limbs and triggering power outages in many suburbs.

The snow, accompanied by temperatures in the low 40s and upper 30s, was the earliest in any autumn this century and the second earliest in the 108-year-old records of the National Weather Service here.

"It's unbelievable," said weather service forcaster Joe Cefaratti.

Dozens of schools closed in Mongomery, Prince George's and Fairfax counties after power outages cut heat and light to school buildings Thousands of school children went home early. Others, locked out of their homes, wandered through neighborhood shopping centers or stayed with friends until their parents could pick them up.

More than 72,000 homes and businesses in the Washington suburbs plus 80,000 more in the Baltimore area lost power for varying periods during the day.

The heating oil and gas distributors were flooded with distress calls from thousands of homeowners unable to start their furnaces as the first cold snap of the season hit Washington along with the snow.

In the mountains west of Washingotn, conditions were worse. Ten to 15 inches of snow in Shenandoah National Park clogged roads, downed power lines and stranded several hundred campers temporarly.

Chief Ranger Larry Hakel estimated 10 to 20 percent of the trees in the park would suffer limb damage from the heavy snows. "They're just breaking by the hundreds," he said.

Cities in western Virginia were hard hit. Harrisonburg had up to 10 inches of snow, Staunton eight inches and Front Royal 5 inches.

Closer in to the Washington area, Vienna measured three inches of snow, and parts of Loudoun County reported four inches. A veneer of one to three inches of snow and slush elsewhere made driving hazardous. Fairfax County Police reported numerous fender-bender accidents with massive morning rush hour traffic jams on rtes. 50, 7, 123 and 236 -- "basically on every main thoroughfare," said police spokesman Warren Carmichael.

The District of Columbia, characteristically warmer than the suburbs because of the so-called urban "heat iland" phenomenon, was not as hard hit hit. Snow fell throughout the city, sometimes heavily, but it never stuck All schools remained open, and there were few power outages because of the storm.

At National Airport, also within the heat island, the weather service officially recorded a trace of snow -- less than one inch. It was the earliest seasonal snowfall recorded here since Oct. 5, 1892, when the measure also was a trace.

Snow has fallen in October here only one other time since the weather service began keeping records in 1871 -- on Oct. and 20, 1940, when a total of one inch was recorded.

Snow rarely falls here even in November. And occurs erratically throughout the rest of the winter. The city averages about 11 days of measureable snow each season but total accumulations vary wildly -- from more than 50 inches in the winter of 1898-99 ton only 2.5 inches in the entire 1930-31 season.

Weather service forecasters noted that yesterday's snow is just a small part of the massive and unusual precipitation that has soaked the Washington area since August. More than six inches of rain fell in September, and almost five inches have been recorded in the first 10 days of October, nearly double the normal amount of 2.66 inches of precipitation for the entire month.

It rained on eight of the first 10 days of October, according to the weather service. River forecasters watching area streams yesterday but said no flooding was immediately in sight.

The weather service called for partial clearing today with temperatures in the early morning from 32 to 38 degrees with a chance of light frost in the suburbs. Highs later in the day should be in the mid to upper-50s.

Forecasters acknowledged yesterday's snow surprised them.

"We were looking for just cool temperatures and some rain," said forecaster Walter Green. He said unexpectedly cold air in a high pressure area over New England was pulled down into the Washington area by a low pressure system over North and South Carolina. "The air was colder than we expected," said another forecaster, "and the rain became snow."

It created incongruous scened throughout Washington yesterday of trees, still in their full green foliage, covered in white. National Park Service chief horticulturalist Jim Lindsey said the snow by itself would do little harm to vegetation. "Only if it freezes will we have a problem," he said.

The snow caused power outages in many scattered areas. Prince George's County was heavily hit. Public schools there were closed two hours early after nearly one-third of the county's 217 school building lost power in mid-morning.

The Potomac Electric Power Co. reported 5,000 homes still without power at 9 p.m. mostly in the southern part of the county. Pepco said some will probably not have power restored until early today.

Similarly all schools in Fairfax County closed an hour early after snow-ladentree limbs snapped and broke power lines in many areas. A virginia Electric & Power spokesman said 1,000 homes remained without power by 10 p.m. e

In the District of Columbia, many city government employes shivered because the heat in most government buildings will not be turned on until Oct. 15.