SOME YEARS AGO, we suggested that the ultimate solution to this city's airport problem was to build a concrete deck over the Potomac River from Little Falls to the Woodrow Wilson Bridge. Nobody took that idea very seriously, although it had obvious advantages: unlimited expansion room for National Airport, runways long enough to handle any airplane and a cover for the river that was, at that time, little more than an open sewer.

We were reminded of that plan the other day when we read about the latest innovation in airline service. American Airlines will inaugurate today a daily flight from National to Dallas/Fort Worth with an intermediate stop at Dulles International Airport. If only our concrete deck plan had been adopted a dozen years ago, American might be able to taxi its plane up the river and across Fairfax County instead of using the extra fuel needed to get it up into the air.

In case you think we're joking, you should know that American Airline is serious about its National to Dulles to Dallas flight. This is the way it has chosen to demonstrate contempt for the Faa's rule that keeps long-haul fights out of National. The rule prohibits direct National-Dallas flights but permits those that make stops in Memphis, Atlanta or, presumably, Dulles.

American's business reasons for observing the letter but not the spirit of this rule is that it thinks it can get a competitive advantage out of this sham. By refusing to carry passanger merely between National and Dulles, American believes it can land and take off faster there than its competitors can at some other "intermediate" airport. And because it regulars customers -- mostly businessmen and politicians -- hate that trip between downtown and Dulles, the airline believes they will perfer its little up-in-the-air-and-down-again flight to the regular non-stop Dulles to Dallas service.

The lesson of the exercise in corporate judgment for transportation planners, both inside and outside the Reagan administration, is that the future of Washington's airports cannot be left successfully in the hands of the airlines. The interests that they weigh in making decisions -- competitive edges, customer convenience, advertising advantages -- have nothing in common with the interests of the majority of the citizens in this community whose daily lives are blighted by the noise and congestion of National Airport.

Forunately, none of the American's competitors has decided -- yet -- to join the ridiculous routing adventure. But if American suddenly gets a surge of passengers, you can bet that they will. In the meantime, we look forward to the next wave of television commercials on which American can feature its exclusive flight from National to Dulles as the visual for its theme song: "doing what we do best."