It is curious that Yuri Andropov, who is 69 and in uncertain health and who has not been seen in public since August, stayed silent for four weeks after the Korean airliner was shot down, and then spoke only in a statement published in his name. Add to that the military's prominence and clumsiness in commenting on the incident in the interval, plus some unusual civilian potshots at its performance. The impression is one of a leadership that does not have its act together.

Harsh, defensive and nationalistic in tone, the Andropov statement on Wednesday appeared to mark the political leadership's full and formal embrace of the marshals' flimsy defense of the shooting down of the Korean airliner. It added to a pervasive feeling in this country that Soviet-American relations are in a deep freeze and arms control is going nowhere. There is a sense, however, in which Mr. Andropov by joining hands with the marshals may have done what a politician must do to move on.

Mr. Andropov spoke sharply of Mr. Reagan, who has spoken sharp words of his own. Though "malicious attacks on the Soviet Union produce a natural feeling of indignation," he said, "our nerves are strong, and we do not base our policy on emotions." Pronouncing himself free of illusions, he suggested, as would a leader who had had to justify why he intended to keep on dealing with Mr. Reagan, that the president had not yet "crossed the mark before which any sober-minded person would stop." The arms race, he said, "can" be terminated; he then went on to criticize in broad and familiar terms Mr. Reagan's latest proposals at the Euromissile talks, "leaving aside"-- presumably, to his negotiators--"the details."

Mr. Andropov warned that the United States is moving into new weapons affecting both strategic stability and the prospects of arms control. It is precisely this perception, of course, that the administration hopes will induce the Kremlin to come to terms. It would be foolish to predict now that agreement will be reached. But it would be a mistake not to recognize that the factors of risk, influence and cost that made the great powers pursue arms control before Sept. 1 apply no less today.

In recognition of the veiled (well-veiled) possibilities kept open in the Andropov speech, the State Department in its otherwise stiff response quietly dropped the previous American insistence on a Soviet apology for the airliner disaster; it continues to seek compensation and cooperation to prevent a recurrence. On the same day, Vice President Bush came through with the long-awaited first American offer to address "somewhere along the line" Soviet concern over the independent British and French nuclear forces.

In brief, it is premature to say that everything was lost when the airliner went down.