For many who read this week's American and Soviet announcements on nuclear testing, there was a sense of having been there before. Arms control began 25 years ago with efforts to limit tests, which were regarded as an impetus to arms building. The movement produced the 1963 agreement banning tests in the atmosphere, but it then stalled, victim of the shared urge to keep modernizing weapons and of the difficulty in arranging terms on which to halt testing underground. Arms control then turned to issues of the quantity and quality of weapons.

Is testing now back as a lead issue? It would be surprising. This week's statements probably are best understood as sparring for position at a moment when the diplomatic calendar features the Hiroshima anniversary, the nuclear nonproliferation treaty review, the Geneva arms control talks and the pending Reagan-Gorbachev summit. Mikhail Gorbachev initiated a unilateral Soviet moritorium on underground testing until the end of the year, to be extended if Washington joins in. President Reagan invited the Soviets to send observers to a Nevada underground test.

The Soviets gave unilateral moratoriums an unforgettably bad name by breaking, with a huge bang, theirs of 1958-61. In current circumstances, only a negotiated treaty could possibly give the United States the confidence to halt testing. And only verification measures more intrusive than any the Soviets have seemed to countenance recently would give the United States confidence in a comprehensive test ban treaty. Such a ban, with no treaty, is what the Kremlin proposes now.

The Reagan administration has always rejected a comprehensive ban, by treaty or otherwise. Notwithstanding its arms-building programs, it still believes the United States is behind. Not all Americans will agree, but the administration does have a second objection. A comprehensive ban would blunt the technological edge that is the chief American asset in the arms control talks. Why give away through a test ban what the Soviet Union should be expected to pay for in arms reductions? This is why a ban cannot be treated as a separate option distinguishable from the proposals on the table at Geneva. Only if talks fail would a testing ban be worth considering.

The administration had thought the Soviets might key a moratorium to the Hiroshima date. It meant to dull the expected propaganda effect by inviting the Kremlin to observe a Nevada test. The proposal underscores the interest of an open society in verifying arrangements made with a closed society. But the invitation places on the Kremlin only a moral burden -- the kind it finds easiest to reject -- to open a Soviet test to American observers, which is what the United States really wants. When we speak of verification, we should be serious.