IN BLUNT, STUNNING detail, Alexandria Mayor and 35-year airline pilot Charles E. Beatley has written a disturbing indictment of flying conditions at Washington National Airport. In addition to presenting what he called "a cumulative sum of National Airport's deficiencies," Mayor Beatley concluded in an article for these pages on Sunday that had Flight 90 flown from Dulles or Baltimore-Washington International, "there is an excellent chance that 70-odd people would be living today and that the Washington area and the whole nation would have been spared the horror . . ."

Mayor Beatley is not known as careless with his words, which is to say that it is appropriate at this point to ask every hard question that so many critics--politicians, pilots, citizens' groups, visitors and residents--have raised about National over the years since carrier jets began streaming up and down its old and heavily traveled runways. Similarly, there are questions about the capability of this region to respond and rescue victims if--heaven forbid--anything like this horrible disaster were to happen here again.

Is National safe enough to stay in business? Not as it has been operating, because--as Mayor Beatley and others who should know have concluded-- this airport has too many "nasty aspects to taking off," even in the best of conditions, to be used in the same way as other airports with longer runways, better Runway Visual Range and safer runway overruns. The fact that for more than 32 years pilots have managed to fly in and out of National without crashing is a tribute to their skills and to those who have assisted them on the ground; but it is not a justification for treating last week's disaster as an unrelated event.

It is the important duty of the National Transportation Safety Board to investigate every aspect of the Flight 90 crash--and, as the board's authorities have noted, to look beyond the accident and the "if-only's" that might have prevented it, to new ways to ensure that such a tragedy won't happen again. If this means calling on Congress and the administration to agree on further reductions in the number, distance or plane sizes of flights to and from National, the board should say so.

In the meantime, those selfish members of Congress who have fought all thoughtful attempts to control the heavy air traffic at National should at the very least have second thoughts. Shouldn't they be thinking of better transportation for themselves, if not for anybody else, to Dulles, via rapid rail above ground?

As for the rescue efforts, they were heroic in every sense; but how well regulated are the water safety equipment standards for rescue teams? Or for passengers and crew in flights over water here? Shouldn't every flight in or out of National be stocked with the most complete water safety equipment, checked on a regular basis? Are the communications networks swift and clear in such emergencies? Shouldn't there be more emergency helicopters at the ready, with rafts, nets and other equipment for immediate drops? Are shock trauma units warned quickly enough to mobilize? What additional equipment might be available from all the armed forces installations in the area?

To raise these questions and seek better flight and rescue operations is not to diminish the remarkable response from authorities and volunteers throughout the disaster and even still. But to learn or do nothing in the wake of this most severe test of air and ground safety would be unconscionable.