By giving all aircraft transponders for Christmas, frequent fliers would not necessarily be buying themselves additional air safety {"Those Close Calls in Flight," editorial, Dec. 11}. The example cited -- the midair collision in August 1986 between a Piper Archer and an Aeromexico DC9 over Cerritos, Calif. -- was found by government investigators to be due mainly to inadequacies in the nation's air traffic control system. Had the Archer been equipped with a Mode C altitude-encoding transponder (the aircraft did have a transponder, and it was on), the accident may still have occurred.

General aviation operators gladly accept requirements that make the skies safer. After all, pilots are the first on the scene of an accident, and they have just as strong a self-preservation instinct as anyone else. It is precisely the possible degradation of aviation safety that has raised our concern about mandatory Mode C transponders in all aircraft.

At many locations around the country, the air traffic control system is already operating at capacity. Computers are strained, controllers are working overtime, and radar coverage is far from complete. By introducing additional information into the system, such as that from Mode C transponders if all aircraft were so equipped, the ability of the ATC system to utilize the information efficiently is questionable. If controllers are forced to "squelch" information because of overload, or if they are dealing with more targets than they can effectively manage, this is clearly not an improvement in aviation safety.

General aviation does not dispute the requirement for altitude-encoding transponders in the airspace around high-density airports. Nor do we object to the use of transponders where they will buy additional safety. But it is placing the cart before the horse to make transponders mandatory in all aircraft in all areas of the country. Our ailing air traffic control system must first be upgraded and proven capable of safely and effectively utilizing large amounts of additional information. -- John L. Baker The writer is president of the Airline Owners & Pilots Association.