A group of airlines that use National Airport, including Eastern Airlines and New York Air, are supporting a controversial proposal that would allow carriers to buy and sell landing rights at the airport.

Months of debate over the plan have deeply divided the committee of 20 airlines that governs access to National. Landing rights at National are now free and are distributed by mutual consent of the airlines' committee. The existing distribution agreement expires on Aug. 31.

This week the committee, unable to come to terms with the buy and sell plan, declared an impasse over who will use the airport after Aug. 31 and turned to the Federal Aviation Administration for help in reaching an agreement.

Critics say the buy-sell approach could raise fares at National by raising the cost of operating a flight there. However, proponents argue that its effect on fares could be beneficial by giving carriers more flexibility to tailor service to demand and operate more efficiently.

Airlines were briefly allowed to buy and sell slots at various airports as an experiment last year. If the plan is adopted for National, it would be the first airport with a permanent buy-sell arrangement with the airlines.

A spokesman for Transportation Secretary Elizabeth Dole called slot sales "one of the full range of options that is on the table." The issue is being decided as the airlines are battling with Dole over her proposal to reduce the number of passengers allowed to use National each year.

To control noise and congestion, the FAA limits airline takeoffs and landings at National to 555 a day. Airlines must obtain a slot for each arrival and departure of a plane.

In recent years, as airlines have multiplied under the 1978 deregulation act and the FAA has placed new traffic restrictions on National, airlines have found it increasingly difficult to agree on dividing up the slots and have been discussing changing the system.

Last year, David Stockman director of the Office of Management and Budget, proposed a buy-sell system for the federally owned airport, but was firmly turned down by then-Transportation Secretary Drew Lewis. The Air Transport Association of America, which represents the major airlines, has also opposed slot sales.

Six to eight of the 20 airlines represented on the committee at National (the 19 airlines at National plus Air Atlanta, which is seeking landing rights there) support some form of buy-sell arrangement, according to committee chairman Nestor Pylypec. Spokesmen for Eastern Airlines and New York Air said they were among the idea's supporters.

"We think it is the fairest way to give slots to airlines that need them," said Theresa Burt of New York Air. "The current system is not responsive to the free marketplace."

Critics, such as Drew Lewis, have held it could increase operating costs at a time of general financial pressure on the airline industry as a whole and could favor bigger carriers at the expense of smaller ones with less cash.

Only three other big U.S. airports have permanent limits on how much traffic they will accept--Chicago O'Hare and JFK and LaGuardia in New York--and have slot systems. But some airlines worry that other airports, taking National as an example, might devise new types of fees for landing rights to ease their own funding problems.

Under one version of the plan being discussed for National, slots would be "grandfathered" to their current holders, who would then be free to sell them to other airlines for whatever price they could get. Another version would have the FAA call in all 555 daily airline slots and redistribute them by auction or lottery.

If the FAA wanted to reduce traffic at the airport, it would buy slots back, at the market price, and retire them.

Deborah Lunn, spokesman for Airport Operators Council International, which represents the major airports, said the group opposes buy-sell at National for now, but members feel such arrangements will become common around the country as capacity problems rise and airports are forced to decide how to divide up access to their facility.