Tens of thousands of turkey-stuffed travelers trying to get in and out of Washington crowded through area airports, railroad stations and bus depots yesterday as the long Thanksgving weekend came to a close.

All afternoon, cars moved like snails through the rain past the rental car lots in and out of National Airport, which by last night was swarming with passengers.

"Horrible," is the way airport parking supervisor Bijan Eghtedari described the scene at National last night. "Nobody can get anywhere. It's just like a big parking lot."

The Sunday after Thanksgiving is traditionally the busiest day of the year at National, and the busiest day at Union Station, too, according to officials there.

Federal Aviation Administration spokesman David Hess said yesterday it will be months before the final tally is in. But he estimated that thousands more than the normal 40,000 arriving and departing passengers would have filed through the airport by the end of the day and that there would be thousands of additional travelers going through Dulles, which normally handles about 6,000 passengers a day.

Despite hectic arrival and departure schedules, operations at National went fairly smoothly until the evening crush turned the main terminal into a zoo. Crowds formed during the afternoon when the conveyor belts poured baggage into arrival areas and at ticket counters shortly before flights took off, but they never lasted long. The only crowd that stayed was the one hunched over miniature airport television sets, watching the Redskins defeat the Eagles.

Seven-year-old Roscoe Thomas, who spent the Thanksgiving holiday with his grandparents in Boston, sat on the floor of the crowded airport terminal guarding the family luggage.

"It's cold up there--in the 20's," said his father before shepherding his family out into the Washington rain.

Pete Lupkins, an American Airlines supervisor, said each of his airlines' 14 flights in and out of National was booked solid, but said there was a high no-show rate, largely because of the rain. "We've cleared stand-by passengers on every flight," he said. "It's not a fun way to travel but it will do."

Tom Dalton and Jim Sauer, two midshipmen from the U.S. Naval Academy in Annapolis who were wearing their navy blue uniforms, sat in an empty corner waiting for Sauer's brother, another midshipman, to fly in from Minneapolis. Dalton was returning from Connecticut, and said he missed his first flight from LaGuardia Airport in New York because of football crowds from a nearby stadium. "The Jets were playing at home today and it was a mess," he said.

Nancy Friedman, a cargo handling researcher in the District, flew in from Rochester yesterday afternoon with her 5-month-old baby Joanna and her husband Philip Beck. The flight was rough, she joked while waiting for her luggage, because all the passengers were heavy with turkey. Everyone in her family, she said, gained "at least three pounds."

Friedman said she expected far worse crowds when she arrived at National. "We make this trip every year and we usually dread it," she said. "But this year it wasn't bad."

At Baltimore-Washington International Airport, crowds were smaller than expected, according to operations assistant Edward A. Klatt. "It's normally the busiest day of the year," he said, but although he had no figures, yesterday seemed relatively quiet. Even the parking lot told the story. "We don't have nearly the amount of vehicles parked here for the long weekend," he said. "In other years, in better times, we had a large overflow of parked vehicles, which we don't have today."

At Union Station, trains bearing homebound holiday travelers started rolling into the station at 6 a.m. "We're running four to six extra cars on every train," said station manager J.R. Lewis. "We're also running five additional section trains in the afternoon."

Lewis said yesterday's crowds were heavier than those departing the city on Wednesday. "Sunday's bigger than Wednesday because everybody's got to get home, and Thanksgiving is our most traveled period."

By the time the 177 from Boston came into Union Station at 12:11 last night, Lewis estimated, the station will have handled about 24,000 more passengers than the 11,000 it normally handles on Sundays.

Holiday travelers who thought they might avoid crowds and confusion by driving to their destinations yesterday were sadly mistaken as cold rain and drizzle fell throughout the day, causing slippery conditions and lengthy backups on area roads and highways.

North and west of Washington, motorists found some roads, bridges and highway ramps coated with ice in the morning and early afternoon.

Highway department trucks rumbled out on the Baltimore Beltway, Baltimore's Jones Falls Expressway and Interstate 70, west of Hagerstown, to salt roads amid reports of a plethora of minor accidents.

A four-mile backup in the northbound lane of the Baltimore Harbor Tunnel was reported during the afternoon. Southbound traffic was also said to be very heavy. The tunnel traditionally handles its highest traffic volumes during the Thanksgiving holiday.