Trains and buses in and out of Washington were crowded yesterday, but National Airport was only slightly busier than usual as negotiations to avert a strike by the nation's air traffic controllers went down to the wire.

Airline spokesmen said there seemed to be a greater number of standby passengers at National than normal, possibly because some travelers were altering their plans and leaving town before a strike, which could begin at 7 this morning if last-minute talks fail.

The airlines had called in extra staff to handle an expected crush of business, but there was no stampede, and the additional standbys were accommodated with problems, the spokesmen said.

Bus and Amtrak officials said they were gearing up for a strike and had canceled vacations for some employes and readied additional equipment.

A.W. Moseley, the assistant terminal manager for the Greyhound Bus Co. here, said that ridership had increased greatly over the last several days.

"Friday was up about 50 percent more than usual," Moseley said, and three additional buses were added to scheduled runs to New York this morning.

The Greyhound central switchboard in Allentown, Pa., which handles calls for the northeastern part of the country, had 5,000 more calls a day in the last few days, according to Greyhound official Camille Ghanayem.

But Ghanayem said many of the callers wanted scheduling information on a contingency basis and it was not clear that many had changed air travel plans at this point.

At National Airport, the scene was decidedly less hectic. Jerry Reedy, an Eastern Air Lines sales agent for the Washington-New York shuttle, said the 1 p.m. shuttle left with 100 empty seats and the next shuttle left with more than 50 empty seats. The shuttle will be canceled if the controllers walk out.

United Air Lines receptionist Nancy Beets said she was asked to work on her day off to handle a feared high volume of passengers rushing to leave town, a crowd that did not materialize. United's 20 daily flights -- which will drop to eight in the event of a strike -- were full, but that was normal for a Sunday afternoon.

"It appears that there is heavier traffic than normal," National Airport operations officer Keith Barnett said, "but no panic as I can see it." Barnett said that he had received no complaints from passengers about being bumped from over-booked flights. Slightly heavier than usual traffic was also reported at Dulles International Airport.

But some prospective travelers said they were leaving the Washington area earlier than anticipated for fear of a strike.

Courtney Hart of Woodbridge said he had planned to leave Wednesday for Omaha to begin a job as a marketing manager for an insurance company. Hart said he changed his plans and made reservations to fly out yesterday for fear that he would be stranded.

Ed Cunningham, general station supervisor in Washington for Amtrak, said that midday trains to New York and Boston were only slightly more crowded than usual. "I think people don't think it's going to happen."

Some, though, like Sam Rhame of Dallas, were not taking any chances. Rhame, vacationing here and planning to leave today for home, was at an Amtrak window asking about schedules -- even though she already has a plane reservation for today.

She was undeterred, even when told that in order to get home she would have to take an overnight train to Chicago and then another overnight train to Dallas.

"I might do it anyway. I hate flying," she said.

Amtrak is also making contingency plans. Vacations for all employes have been canceled, extra food is being stocked and an additional 24 cars are ready for service on the East Coast in the event of a strike, according to Mike Delaney, an Amtrak official.

"Every piece of equipment that doesn't have safety problems is being called up," Delaney said. There are about 400 cars operating on the Boston-Washington corridor, he said, so the increased capacity is only about 6 percent. "We just don't have a lot of excess capacity," he said.

Delaney said he was confident Amtrak could take up much of the slack, but only for about two weeks. After that, some of the cars will have to be taken off the line for servicing.

While the large transportation carriers prepare for the worst, individual travelers and smaller carriers are also gearing up for contingencies.

Rental car agents at National Airport said customers on arriving flights from as far away as Ohio are asking about driving home in the event of a air traffic controllers' strike.

Smaller bus lines are also planning service directly from downtown hotels to hotels in New York.