ISN'T IT marvelous? With one of the world's great airports sitting practically vacant out in the Virginia countryside, the airlines are squabbling over who gets to fly when into National Airport. More of them want to fly more planes into National than are authorized to operate there. Many of them want to fly no planes into Dulles. a

That's the situation Secretary of Transportation Neil Goldschmidt now faces. The airlines can't agree among themselves, as they have been doing for some years, about operating rights at National and have asked him to arbitrate. He is to try to fit into that already overcrowded airport the planes of three new airlines -- New York Air, Midway Airlines and Air North. He is also trying to find operating rights for Texas International so it can start its proposed shuttle service to New York. And he needs to accommodate the winter increase in the flights of the established airlines. In total, Secretary Goldschmidt has been asked to figure out how 23 airlines can fly more than 350 planes in and out each day at an airport that is now limited to 320.

What should he do?

Well, we know one thing he should not do. The number of daily operations at National should not be increased -- one commercial airliner over the Potomac River every 90 seconds, on averages, from 7 a.m. to 10 p.m. is enough.

The one thing Secretary Goldschmidt should do, of course, is something he wouldn't dare try. That is to start cutting off cities from the list that National now serves. It makes little sense for an airline that wants to compete for National-New York traffic to have to compete first for operating rights with flights from National to Miami, St. Louis and Chicago.

National ought to be a short-haul, commuter airport with any flight of less than 500 miles getting priority over every flight of more than that distance. In fact, one bold move -- transferring all Chicago flights to Dulles -- would solve all of National's problems, probably forever. But it would also result in, if not Secretary Goldschmidt's being ridden out of town on a rail, scores of congressmen, hundreds of airline officials and thousands of businessmen in hot pursuit.

There's another thing Mr. Goldschmidt might think about, although he probably couldn't get away with it, either. That's to tell the big airlines that the number of slots they get at National depends on how many flights they operate at Dulles. Eastern, which flies more planes in and out of National than any other airline, has zero flights at Dulles. Five big-name airlines -- Eastern, Delta, United, American and TWA -- have 149 flights out of National each day (almost half the total) and 17 out of Dulles. Is it any wonder Dulles sits in such isolated splendor?

There is, to be truthful about it, no easy solution to the current problem at National. Nor is there going to be any easy (or right) solution to that airport's problems until Secretary Goldschmidt, Congress and the airlines rid themselves of the idea that National is and must always be this city's major airport. It's time that all of them accepted Dulles for what it was intended to be -- a major, busy airport -- and stopped quarreling over which airline gets to generate the noise that disrupts the life of the city.