AS LONG AS National Airport continues to exist, the rules that should guide its development are clear. The runways should be closed at night and the number of operators permitted during the day sharply limited. The airplanes permitted to use the airports should have the most efficient noise-suppression and anti-pollution engines available. And commercial airliners serving nearby communities should have priority over those serving more distant cities in the competition for operating rights.

The proposals for a new policy for National, now on the desk of Secretaty of Transportation Brock Adams, meet the first two tests but fail the third spectacularly. The Federal Aviation Administration has recommended that the ban on flights of more than 650 miles into National be lifted. In this era of deregulation, it argues, each airline should be allowed to decide which of its flights will operate at National and which whill operate at Dulles or Baltimore-Washington.

But what would be the result? As soon as one airline used one of its assigned slots at National flight to, say, Denver, its competitors would feel compelled to do the same. And each long-haul flight moved into National would either replace a short-haul flight or fill a slot that might be used for one. If the demand for short flights is inadequate to fill National to capacity now, the slots should be left vacant and the noise and air pollution generated above the Potamac River reduced.

The brief travel time from dwontown Washington to National-the only valid reason for the airport's continued existence in so densely populated an area-is far more important on short flights, used mostly by commuters, than on long trips. The airport should eventually serve only nearby cities, and the FAA should be working to shrink the geographic area the airport serves-not trying to enlarge it.