It is 6:15 on a Friday evening. Business travelers clutching briefcases and bulging overnight bags form a weary column that snakes out of sight in the long corridors of National Airport as they wait for seats on the Eastern Airlines shuttle to New York.

Those nearing the gate arrived an hour earlier to find two planeloads of people ahead of them. Now long faces perk up as an Eastern official strides past with news of the next plane to depart: "The airplane is off has left New York," he announces. "You should be away from here by 7:20, 7:30."

Many of the people gathered there that night last week would wait 2 1/2 hours to fly to New York, as the Federal Aviation Administration limited shuttle take-offs to one an hour (three hourly is common in normal times). Some 200 people would not be able to fly at all, according to an Eastern spokeswoman.

It was among the shuttle's most chaotic days since air traffic controllers walked off their jobs two months ago -- and things had improved markedly yesterday, Eastern reported. But it was proof that travelers stepping into National and airports around the country these days can't be sure when they will be airborne.

For the present, there is no end in sight to these strike-induced delays. Training new controllers to replace the 12,000 who were fired will take two years, the FAA says. The short-term outlook is dim too -- snow and freezing rain which tie up airports every year are not far off.

Only about 2.5 percent of the nation's scheduled flights have been delayed by 30 minutes or more this month, the FAA says. But the delays are concentrated on the East Coast, affecting Washington area travelers disproportionately, especially on the route to New York.

Passengers seem to be taking it in stride, rearranging their personal and business lives, flying during nonpeak hours, or simply waiting out the delays. The Dallas-based Airline Passengers Association, composed mostly of business travelers, reports that travelers are "very, very patient."

"What can I tell you? I'm in a line that goes 18 blocks," said Dan Nichols, a New York tax specialist trying to get home last Friday aboard the shuttle. "You get used to it. You don't expect to get out on time . . . You tell your wife you'll be home sometime between six and midnight."

C.J. Jones, a U.S. Labor Department official who travels weekly from his Chicago home, tries to schedule flights on off-peak hours. Instead of flying to Washington on Monday morning, when delays are likely, he breaks his weekend and goes Sunday evening, when the schedules are more reliable.

During off-peak hours, airplanes generally can take off and land on schedule at the 22 major airports where the FAA has restricted flights because of the strike. The back-ups generally come during the mid-morning and late afternoon, when the public wants to fly and airlines try to concentrate their take-offs.

Delays are generally caused not by controller shortages in airport towers but by thin staffing at the FAA's 20 enroute control centers, which guide planes after they leave the immediate vicinity of the airport from which they take off.

The centers for the New York and Chicago areas, for instance, were among the hardest hit by the strike. They now have laid down strict limits on numbers of planes per hour that they let neighboring centers feed into their areas of control.

Short staffing at these two centers has helped concentrate delays in the East. For example, last Thursday, one of the busiest days of the week, 394 delays of 30 minutes or more were recorded, according to FAA spokesman Fred Farrar, with 120 occurring at La Guardia and 46 at National.

In September, delays apparently worsened somewhat in the Northeastern corridor, as traffic levels grew beyond what the FAA had planned. This traffic growth did not compromise safety, as planes remain on the ground until they can be safely taken into the traffic control system, according to the FAA.

The upsurge in traffic was felt strongly at the Washington area enroute center in Leesburg. The center began the strike handling about 75 percent of normal traffic but on some recent days traffic has reached 100 percent of normal levels.

The FAA cites several causes for the upsurge: FAA schedulers being too quick to approve new flights; private plane pilots bending rules by taking off on visual flight rules and then requesting ground control from mid-air; and air carriers operating ground-controlled flights not specifically approved. Last week, the FAA ordered minor reductions in flights.

Delays will continue indefinitely, however, though FAA officials say they could easily eliminate delays simply by scheduling flights on off-peak hours. Many airlines favor the existing system, which allows them to advertise flights at the high-demand time, even if the planes consistently leave 30 or 60 minutes later.