WASHINGTON (AP) _ The Federal Aviation Administration should curtail scheduled airline traffic to ease the pressure on overworked air traffic controllers, according to a new congressional study.

Congressional sources said the study by the General Accounting Office, the investigative arm of Congress, concludes there are not enough experienced controllers to handle today's traffic loads.

The report also says that plans to increase the controller work force are being hampered by stepped up retirements and training problems, the sources said.

The FAA has 14,000 controllers in airport towers and 20 en route air traffic control centers around the country. Transportation Secretary Elizabeth Dole has promised to add another 1,000 controllers in the next two years to meet the needs of future traffic growth.

But Mrs. Dole and FAA Administrator Donald Engen repeatedly have insisted that there are enough controllers to handle current traffic needs. They said that when there is a question of controllers being overburdened, flights are held back through traffic flow controls.

But the GAO study, according to congressional sources who spoke on condition they not be identified, concludes that there are far fewer experienced controllers available than are needed, especially during peak travel periods and in parts of the country where the skies are particularly congested.

The study, much of which is based on questionnaires sent to 5,500 controllers and supervisors and some interviews and letters from controllers, is expected to be released this week.

It was prepared for the House Investigations Subcommittee of the Public Works and Transportation Committee.

Rep. Guy V. Molinari, R-N.Y., a subcommittee member, declined to discuss details of the report, but said it generally substantiates that ''serious problems'' remain in the air traffic control system.

Molinari last year called on the Reagan administration to rehire some of the controllers fired after the 1981 strike. Several senators have made similar requests, but legislation calling for rehiring of some controllers has gone nowhere in Congress.

The administration has argued that those former controllers would also take months to retrain and that they might cause friction in towers and control centers where controllers who ignored the 1981 strike continue to work.

Some of the findings of the GAO report, such as the belief by many controllers that they are handling too many planes, were disclosed last summer by GAO officials during testimony before congressional committees examining air safety.

But the GAO has not previously announced any conclusions or given any recommendations on what might be needed to alleviate the problem.

''They're reinforcing what they've said in the past - that the controller work force is spread too thin and they're being overworked,'' said one source.

The report suggests there may be no alternative to reducing air traffic flow because it takes many months to put new, experienced controllers into towers and control centers, according to the sources.

The airline industry has opposed FAA restrictions on traffic, arguing the free flow of air traffic is needed during a time when customer demand is increasing and airlines are fighting to compete. The airlines for more than a year have called on the FAA to step up its controller hiring plans.

Earlier this week at a congressional hearing in New Jersey, several controllers warned of potential safety problems because of their workload.

''We are stretching our meager resources to the breaking point,'' testified Robert S. Bell, a controller at the New York terminal radar facility at Westbury, N.Y.

The hearing was held in Cliffside Park, N.J., near where a business jet and small private plane collided last November, killing six people. While the cause of the collision has not been determined, the investigation has revealed that a controller handling the two planes gave an erroneous direction of flight for one of the planes involved.