ONCE AGAIN, American Airlines is doing what it does worst--taking advantage of the fine print to get around the obvious intent of the rules limiting air traffic at National Airport. In 1981, American established flights that went, with a hop, skip and jump, from National Airport to Dulles and then all the way to Dallas-Fort Worth, an attempt to get around the mileage limitations that prevent a nonstop National-DFW flight but provide service to those who want to leave from National and go to northern Texas. Now American has announced it will send two flights into National after the 10 p.m. curfew for jet flights, even though local residents were assured that that would never happen.

The culprit here is the fine print and--so far--the complacent attitude of the Federal Aviation Administration. When former transportation secretary Drew Lewis was drawing up the noise rules for National, he assured everyone that no jet would be quiet enough to be allowed in after 10. Now it turns out that McDonnell-Douglas' DC-9 Super 80 met that standard in November 1981. It took American Airlines, with its damn-the-torpedoes, full-speed- into-National attitude, to take advantage of this unexpected result and schedule flights into Na- tional, one of them scheduled to arrive after midnight, direct from Baltimore-Washington International.

Others may follow. Trans World says it wants to change the scheduled arrival of a flight from St. Louis from 9:59 p.m. to some time after 10. That's a recognition, whether TWA wants to admit it or not, that many of the scheduled arrivals of 9:59 and 10 at National are entirely fictitious, and the FAA has allowed airlines at least a half hour's leeway to let them land. Other airlines may see whatever competitive advantage American discerns, and follow along.

The FAA's attitude now is to leave the regulation and the airlines well enough alone. The noise levels were set to a standard that supposedly wakes only one in 10 people sleeping inside their houses: let them be awakened again and again, the FAA seems to say, and let others have their indoor and outdoor activities disturbed far more often and significantly later than anyone contemplated when the rule was established. Horsefeathers. The rule should be rewritten to do what it was intended to do: keep jetliners out of National after 10. Secretary of Transportation Elizabeth Dole, who has done yeoman's work on National's problems, is on vacation now. When she gets back, we hope one of her first orders of business will be to stop American's end run around the intent of the National rules.