WE APPLAUD the decision by 28 American physicists to cancel their participation in various aspects of the Soviet-American scientific exchange program. They acted to protest the punitive sentence handed down to Soviet physicist Yuri Orlov for "slandering" his government by checking on its observance of its human-rights pledges at Helsinki. They meant, too, to make the Kremlin think twice before further persecuting two other Soviet scientific figures, Anatoly Scharansky and Alexander Ginzburg, whose fates are currently in the Kremlin balance.

No one aware of the care with which participating American scientists have nursed the exchange program for two decades can fail to appreciate how difficult it must have been for the 28 to step back. The program has provided to its thousands of participants a special window on Soviet science and, beyond that, a special opportunity to work quietly, if no uncertain effect, for the gradual liberalization of a sensitive and elite corner of Soviet society. It is particularly the latter opportunity that has led most American scientists to swallow their sure knowledge that scientifically the Russians were getting a good deal more out of the exchanges than the Americans, and to mute their objections to Kremlin violations of the human rights of Soviet scientists. The exchanges constitute the single part of Soviet-American relations in which individual Americans - not the government, and not the National Academy of Sciences, which administers many programs - control participation and content. Prizing this channel, most participants have been loath to jeopardize it by allowing politics to intervene.

The Soviets remain as eager as ever to piggyback on advanced American science and technology - to gain the immediate fruits and, on another level, to spare themselves the need to create the conditions of free inquiry that would give the backward areas of Soviet science (most of them) the chance to catch up. They have played cynically, but with broad success, on the American desire to keep the exchanges going, no matter what the cost.

But among American scientists the conviction is spreading that it is impossible to sustain exchanges in conditions of Soviet repression. Concern continues over the denial of rights, including the right to emigrate, to scientists of Jewish origin, and concern mounts over the denial of rights to Soviet scientists across the board. It is not that a campaign is being organized by the administration or the national academy. Indeed, administration and academy figures have repeatly warned Moscow that they have no authority over the decisions of the individual American participants. In American eyes - the Russians may be blind to it - the scientists' reaction takes on more, not less, force from the fact that it is of private origin.

Sen. Robert Dole (R-Kan.) has just introduced a resolution calling for an administration review of official scientific exchanges, to continue until the Kremlin complies with the Helsinki provisions. Given the initiative now being displayed by American scientists, however, we don't think this is the right time for the government to get into the act. The difference between the Soviet and American scientific communities is the difference between official control in the one and individual choice in the other.Americans have an alternative to putting the scientific community into political harness. It is for scientists to act on their political responsibilities themselves.