Flight schdeules at Washington National Airport appeared to be returning to normal yesterday after a wildcat air traffic controller's lowdown but aviation sources said there is a strong possibility of natonwide disruptions just before the Thanksgiving holidays.

Delays at national yesterday were running about 15 to 20 minutes on some flights, but many were on time and the disruptions were minimal compared to the 30minutes on some flights, but many weretwo-hour delays airlines experienced thursday.

"Everything is on schedule now: we have no delays." John F. Stiffler, who is in charge of Eastern Airlines operations at National, said after the evening rush yesterday. In late morning, Stiffler had reported a consistent pattern of 15 to 30-minute delays.

The Federal Aviation Administration, which operates the air traffic control system, admitted yesterday after a formal inquirty at National that " a slowdown by some controllers" had occurred a fact that was obvious to air travelers.

John Thornton, president of the ProfessionalAir Traffic Controllers organization (PATCO) local at the National control tower, denied there had been a slowdown. "The guys were just kind of down in the dumps." Thornton said because the Civil Service Commission ruled that National Controllers did not handle enough traffic to win promotion to a higher-paying grade. The decision will cost National's controllers about $5,000 a year and is being appealed.

Thornton and other controllers interviewed insisted that there was no PATCO action involved at National: the same assertion was made by John Leyden, national PATCO president. "If there is an action at National ," he said, "it does not have PATCO sanction."

The last thing Leyden needs or wants right now is a wildcat slowdownn PATCO's contract with the FAA expired in July and negotiations on a new pact were broken off in September, although there have been some informal FAA-PATCO contracts since then.

PATCO, according to Leyden, has scheduled "information pickerting" at major airports across the country sometime before Thanksgiving. Nov. 24. "It will be strictly informational" Leyden said. "No job actions are planned."

At another point during the telephone interview, how ever, Leyden said, "You're going to have a problem on the 21st (of November) if we don't have a contract."

There is something of a tradition in the U.S. of air traffic slowdowns during high-visibilty periods such as Thanksgiving and Christman, when the holiday traveler is added to the normal business traffic.

Knowledgeable officials in both the FAA and PATCO.(See CONTROLLERS, B4, Col.1)(CONTROLLERS, From B1)while cautiously expressing hope that a new agreement can be reached without major difficulty, said that slowdowns at some major centers such as Chicago or New York are possible. Because of the repple effect of such actions, that would mean delays throughout the national air traffic system.

There are a number of unresolved issues separating labour and management, but the most important of them is a demand by controllers that those with seniority have first call on vacancies nationwide.

At the moment, vacancies are filled in whatever way the FAA finds expedient--through on-site promotion or transfers. According to Leyden, his controllers want the right to bid on vacacies.

"That way a guy who has really been up against it in New York, for example, could go to a less-intense" air traffic facility, according to Leyden.

Other issues include the restoration of a clause that gives contoration of a clause that gives controllers immunity from certain disciplinary actions if they report unsafe conditions in which they were involved, and a reduction in the number of on-the-job trainees who are used in slots for full controllers. CAPTION:

Picture, Jetliners line up waiting for takeoff from National Airport. Air traffic controllers in the tower, who staged a wildeat slowdown Thursday, appeared to be returning to normal. The slowdown concerned contract dispute. By Larry Morris - The Washington Post