The first snowstorm of the season crept into the Washington area at the start of last evening's rush hour, snarling traffic and spawning hundreds of accidents as a prelude to what is expected to be an even more miserable rush hour this morning.

The storm was expected to dump four to six inches of snow across the area.

The precipitation changed to freezing rain and sleet in many areas early this morning, and was expected to turn to just rain later in the morning.

Forecasters with the National Weather Service predicted that the storm would move out of the area by midmorning, and that by this afternoon temperatures would climb to about 40 degrees.

Officials said the bad conditions early today may be partly offset by the large number of people who have taken this week off and by the fact that schools are closed for their winter breaks.

No deaths or serious accidents were attributed to the storm in the immediate Washington area last night, although a 22-year-old Roanoke County man was killed when his car slid across snow-slick Interstate 81 and struck a pickup truck in Botetourt County, Va.

But the snowfall did produce a rash of less-serious accidents here, resulting in so many reports that police in Maryland and Virginia said they couldn't record them all.

Officials in both states last night reported traffic delays of three to four hours on some main arteries. "It's extremely bad. Just a mess," said a Virginia State Police dispatcher.

Streets in the District remained slick early this morning. Tara Hamilton, a spokeswoman for the D.C. Department of Public Works, said the city had 84 trucks out salting major roads, but that officials believed there was not enough accumulation for the streets to be plowed.

Virginia State Police spokeswoman Lucy Caldwell said some motorists had become so flustered by the slippery roads that they abandoned their cars along highways during the evening rush hour. She said the state imposed a snow emergency at 5:30 p.m. "to keep the roads clear for traffic."

Operations at Dulles, National and Baltimore-Washington International airports were disrupted last night while runways were cleared of snow. National Airport closed for 45 minutes and BWI was shut for an hour, officials said.

Metro spokeswoman Marilyn Dicus said the rail system will operate this morning on a modified rush-hour schedule, with the frequency of trains slightly lower than usual but with longer trains.

She said a decision was to be made at 5 a.m. on Metro bus service for the day. If road conditions are poor, Metro will go to a snow emergency route operation, with buses on major roads only.

The spokeswoman said Metro's information line will open at 6 a.m. Its number is 202-637-7000.

But what some commuters saw as a nightmare was viewed by others as simply a White Christmas that came a couple of days late. As soon as there was enough snow on the ground, children began fashioning it into snowballs and snow sculptures and grabbing everything from sleds to pieces of cardboard for an evening of sledding.

The winter storm began covering the area with snow at midafternoon, exactly on the schedule forecast by the National Weather Service. The advance notice meant that highway crews were waiting.

"We have the trucks ready to go. We are ready," Dolly Allen of the Maryland state highway department declared hours before the snow arrived. When the first flakes fell, 81 crews began plying the roads with salt and sand in Montgomery County, and 67 crews began working the trucks in Prince George's County.

All area jurisdictions reported a similar state of readiness. The District put its snow emergency plan into effect at 3 p.m., before the first snowflakes were seen.

While the snow emergency is in effect, the owners of cars parked along emergency routes may be issued $100 tickets and assessed the cost of towing. As of last night, D.C. police had ticketed 850 cars and had towed 90, said Hamilton, the public works spokeswoman.

Parts of two streets in the District were shut last night for safety reasons, Hamilton said: Constitution Avenue NE between Louisiana and First streets near the Capitol, and the exit ramp to South Capitol Street from the eastbound Southeast Freeway. She said it was unclear when they would reopen.

Metro also was prepared for the storm, said spokeswoman Beverly Silverberg. Switch heaters and heaters for the third rail had been checked and special plows and scrapers had been readied, she said. Plows and trucks to keep Metrorail parking lots clear also were standing by, Silverberg said.

But the rush of outbound motorists and the heavy snowfall meant that crews weren't able to spread salt quickly enough to prevent the evening's slippery conditions. And police officers weren't able to respond quickly enough to accidents to prevent major tie-ups.

"We've got a lot more accidents than we have officers," Virginia's Caldwell said early in the evening.

The afternoon snowstorm was no surprise to forecasters. National Weather Service officials said that it started snowing in the upper atmosphere at 9 a.m., but that the snow evaporated before it reached the ground because of the dry air near the Earth's surface.

"But planes above 4,000 feet up to the base of the clouds at 6,000 to 8,000 feet have been having trouble all day," said forecaster Valerie Thompson. The flow of moist air from the southwest later in the day allowed the falling snow to reach the ground.

That same flow of air will put an end to the storm by this morning, Thompson said.

That was little comfort to motorists last night. William Green, 43, an insurance salesman from Greenbelt, left work early in a vain attempt to avoid the snow.

"Every year we get a snowstorm and every year I find that I'll never get used to driving in the snow," he said.

Staff writers Michele L. Norris, Ruben Castaneda, Robert O'Harrow Jr. and Brooke A. Masters contributed to this report.