The recent exchange of charges of lying between President Reagan and Yuri Andropov over Soviet SS20 missiles has left a bitter residue. Few people even knew the concrete issue that precipitated the charges. The exchange was seen as merely a manifestation of the deterioration of relations between the two powers, and most people here assumed the president must be right--not so much because they had confidence in his assertions perhaps as because they lack confidence in what the Soviet leaders say.

What was the issue? It was whether the Soviet unilateral moratorium on additional SS20 deployments, announced with some fanfare by Leonid Brezhnev a little over a year ago, had in fact been carried through. Reagan, on March 23 of this year, said that the Soviets had increased the number of SS20s despite the fact that "Mr. Brezhnev pledged a moratorium, or freeze, on SS20 deployment. "Some freeze," he added ironically. Andropov responded on March 26 that Reagan had "uttered a deliberate untruth in asserting that the Soviet Union does not observe its own unilateral moratorium."

What has happened to the Brezhnev moratorium? Brezhnev had announced on March 16, 1982, a Soviet decision "unilaterally to place a moratorium on the deployment of medium- range nuclear weapons," specifically to "freeze" the replacement of older SS4 and SS5 missiles by SS20 missiles "in the European part of the U.S.S.R." The moratorium would last either until agreement in negotiations or until the United States went ahead with "practical preparations to deploy Perhsing II and cruise missiles in Europe." The statement was not precise on the terms of this freeze--a vagueness that was later to reduce considerably the impact of the action on Western opinion, which had, of course, been its target.

After the initial reports on it, the moratorium drew little comment in the West until a spate of statements by American officials in September and October to the effect that the Soviets were ignoring and not abiding by their own moratorium, since new SS20s were being deployed as before. Accounts referred to SS20s being added at a rate of "one a week." Reagan said so on March 23 of this year and again, after Andropov's rejoinder, on March. 31. No references were made to the fact that the moratorium had been limited to the European part of the Soviet Union.

At the time of Brezhnev's statement, the Soviet Union had deployed 207 operational SS20 launchers within range of Western Europe (on both sides of the Urals), and 297 overall. From August 1982 to February 1983, an additional 54 launchers became operational, for the present total of 351, of which 243 are within range of Western Europe. In other words, since the moratorium, 54 additional SS20 launchers have become operational. That fact is the basis for the administration's charge that the Brezhnev moratorium was a sham.

It is also true, however, that at the time of Brezhnev's declaration, the Soviet Union had, operational and under construction, a total of 351 launchers, with 243 within range of Western Europe. If deployment is defined to count those operational and those under construction, the moratorium has been abided by. No new SS20 launch sites "in Europe" (or even within range of Western Europe) have been added to those existing--operational and under construction--at the time of the declaration of a moratorium.

Reagan and other administration spokesmen continue to say that the Soviets are still adding an SS20 per week. In fact, that is no longer true. The number under construction means the total this yar will be far less than one a week. The implication that those missile launchers still under construction--all in Eastern Siberia --affect the military balance in Europe is misleading.

No administration spokesman has acknowledged either that deployment vis-Ma-vis Europe has stopped or that no new SS20 deployment vis-Ma-vis Europe began after the moratorium was announced.

It is quite clear that the Soviet interpretation of the moratorium meant no further SS20 deployments, in substitution for older missile launchers, beyond those already under way when the moratorium was declared. Yet the administration, aware at some levels (almost certainly not including President Reagan) of the actual situation, has repeatedly told European and American audiences that the moratorium was a fraud.

The administration might better have argued that the moratorium meant less than met the eye, since it was probably proclaimed only when the Soviets had met their planned level of deployment, that some 36 more launchers facing Western Europe were being completed even under the moratorium, and that the moratorium did not apply in the Far East.

But while the shortcomings of the Soviet action are fair game, the moratorium based on the Soviet interpretation of an end to further deployments in Europe was not a sham. They did stop SS20 deployment vis-Ma-vis Europe. Moreover, while it was a unilateral moratorium, it was in the pattern set by the Soviet-American SALT I interim agreement in 1972, when a freeze was placed on new construction of ICBM launchers, but those already under construction could be and were completed.

Since the Soviet moratorium on further SS20 deployments in (and facing) Europe is not a sham or a lie, to suggest as much was, as Andropov stated, "an untruth."

The moratorium, under the conditions set forth by Brezhnev, may be ended at any time, since "practical preparations" for deployment of the Pershing II and GLCM missiles are actively under way. If so, the limiting conditions could properly be recalled, but it should not be said to have been "broken" by the Soviets.