THE POLICY for National Airport announced last month by Secretary of Transportation Neil Goldschmidt was -- despite its shortcomings -- comprehensive and understandable. The revisions of that policy recommended to Congress Wednesday by a conference committee have neither characteristic. They make a shambles of what Mr. Goldschmidt was trying to accomplish and provide a remarkable demonstration that the members of the committee don't know what they're doing.

Mr. Goldschmidt attempted to find a policy that met two goals. One was to keep National, and the ground trasnportation network serving it, from being totally overwhelmed by passengers (as if it were not already). The other was to provide this community with some (much too little) relief from the noise of airliners blasting up and down the river.

To achieve that, Mr. Goldschmidt proposed opening National to the new and supposedly quieter jumbo jets and putting a permanent limit on the number of passangers it will handle. These two steps would, in the long run, reduce the number of flights -- and hence some of the noise -- since 17 million passengers will fit into fewer big planes than the number of smaller ones that now fly in and out of the airport. To help the flight reduction along (and to keep the airlines from cheating on the passenger total), Mr. Goldschmidt proposed to cut back by 10 percent the number of airline flights permitted each hour and to shorten the number of hours the airport is open each day. He noted that the number of hourly flight would have to be reduced at future dates to keep the passenger limit intact.

So what did the conference committee do? It approved all of the proposal except the reduction in the number of hourly flights. Thus it removed the key element for enforcing the passenger limitation or, at least, spreading the passenger load throughout the day. That, in turn, prevents the rest of the policy from achieving the goals it was designed to meet.

If the airlines can simply substitute one big plane for one smaller one, they can bring in more people each hour. That means either the passenger limit will be exceeded quickly -- perhaps in 1982 -- or, if it is enforced, most passengers will use the airport during peak travel hours.Either way, the airport -- not to mention the highways near it -- will be swamped during part of the day.

This contradictory and illogical action of the conference committee grew out of the fear of many members of Congress that flights from their home towns are going to be shifted from National to Dulles or Baltimore if Mr. Goldschmidt's proposal goes into effect. The fact is that the only way to those flights -- from, for example, Dayton and Charlotte -- can be kept at National is to drive other, more profitable flights out of there. Yet the committee voted to open National, for the first time in more than a decade, to flights from such places as New Orleans and Kansas City.

All this points to the conclusion that there are very few members of Congress who understand either the problem of National Airport or the economics of a deregulated airline industry. All most members seem to understand is that they and the people back home prefer to fly into National rather than inot Dulles or Baltimore, and that preference is far more important to them than the environment of this community or the rationality of an airport policy.

At this point, however, they should take a look at the chaos the policy proposed by the conference committee would create. That policy is a sitting duck for misinterpretation and litigation. Either Congress should let Mr. Goldschmidt's policy go into effect or its members should learn something about National Airport (beyond where it is) before tampering with it.