The United States, in the matter of Soviet Foreign Minister Andrei Gromyko's nonattendance at the U.N. General Assembly session opening today, has shot itself in the foot.

It was definitely in the American interest to have Mr. Gromyko show up as usual in New York. There he would have been exposed firsthand to the views of other nations and great numbers of citizens about the shooting down of the KAL airliner and his government's arrogant conduct afterward. Those views could, and no doubt would, have been made abundantly plain to him--and everyone else--while his safety and security would have been guaranteed.

Very few people on the American side, however, seem to have acted in terms of this plain American interest. The governors of New York and New Jersey and the local airport authorities, who are no more experienced in foreign policy than they are in brain surgery, evidently thought they would be striking a blow for, well, something, by banning the Gromyko plane. Some part of the administration then got into the act by determining that the Aeroflot boycott could not be bent even for the customary noncommercial flights carrying the Gromyko party. That determination produced the bizarre invitation to fly a Soviet military plane to an American military field. It is not clear whether officials ever realized that they were handing Mr. Gromyko a ready-made excuse to keep out of a setting that promised to be extremely uncomfortable and embarrassing for him.

As a result the administration was left on the defensive, explaining why, in its view, it had not violated the longstanding American "headquarters agreement" with the United Nations: "The Federal, state or local authorities of the United States shall not impose any impediments to transit to or from the headquarters . . ." And the Soviet Union, which is working intensely to convince the world that the United States seeks to exploit the airliner incident for nefarious political purposes, was given a gift contribution for that campaign.

From being the party in the dock for downing the airliner, the Soviet Union cannot so easily slip into a role, in the lesser banning incident, as the injured party. It was clumsy of the United States, however, to give it any opening at all.