What do we risk if the weights of Afghanistan and Sakharov pull down the curtain on two decades of laboriously cultivated Soviet-American collaboration in science, engineering and health care?

The answer is: precious little in science engineering or health care; a unique window, cloudy though it might be, on some of the innards of the Soviet research enterprise; and, finally, the worthy expectation that the brotherhood of science can smoothe perilous political differences.

The first victim in this sector of the suddenly soured East-West relationship is the diehard belief that the Soviet Union's top scientists are somehow nicer guys than the political bosses they serve. Perhaps they are. But this American-held perception, derived mainly from ceremonial comings and goings and toast-drenched banquets with Soviet counterparts, is also linked to the notion that because the modern state finds scientists indispensable, it must necessarily accord them political tolerance and influence.

For years, a major prop for this belief was the regime's tolerance -- albeit harsh and grudging -- of Andrei Sakharov's loud dissents. Our scientific establishment's explanation for his continued ability to speak out was that the renowned physicist was under the protective wing of the Soviet scientific leadership, which revered him as a superstar of research and one of its own. From this followed the argument that this shielding of Russia's leading dissident merited the encouragement of professional collaboration with American colleagues.

The Sakharov banishment has struck the American scientific leadership with the emotional impact of the Oppenheimer persecution of 25 years ago, and the direct effect has been a wave of anti-cooperation sentiments that are rapidly taking effect on a broad array of activities ranging from cancer studies to conferences on construction techniques. Does the turnabout matter? s

From the perspective of enriching American science and technology, the return on collaboration has been slight, though not altogether inconsequential. rAs White House science adviser Frank Press told a congressional hearing last week, pioneering Soviet experiments in the expensive field of nuclear-fusion research gave a boost to our own now-well-advanced program; and we've learned from the Soviets in some other fields, among them waste-treatment technology, which Press said has saved the United States an estimated $55 million in research costs. But given that the United States now spends -- in government and private funds -- about $60 billion a year on research and development, the claimed savings from collaboration are piddling.

As for getting the Soviets hooked on our recognized leadership in many fields of science, the fact is that, obviously in fear of the cutoff that is now actually occurring, the Soviets have not risked dependency on Western science and technology. They take what they can get and wangle for more; but it it were all turned off tomorrow, it's clear that they could get along satisfactorily for military, industrial and health purposes. In some cases, such as ice-breaking technology and certain fields of energy research, the Soviets have gagged on the show-and-tell reciprocity requirements, and collaboration has been called off.

What we're losing, then, is not much scientifically. And as is evident from Soviet selectivity on the subjects, the much-sought-after, but little discussed, opportunity that collaboration provides for studying Soviet research from the inside is something that our Soviet teammates carefully regulate.

What's left, though in extremely tattered condition, is the hopeful belief that the Soviet scientific establishment is, in fact, a moderating force in that nation's political and strategic affars. In the punish-the-Russians mood that is currently flourishing, it is difficult for this evaluation to be taken seriously. Which is why attention ought to be given the countercurrent views expressed at a congressional hearing last week by one of the world's grand old men of physics, Victor F. Weisskopf, professor at the Massachusetts Institute of Technology:

"I believe that it is important that the United States uphold the principle that science belongs to all humanity and stands above the vagaries of political strife. . . . We should not lose contact with one of the best elements of Soviet society, with a group which basically agrees with our value scale and -- in contrast to the avowed dissidents -- who may have a significant influence on the future developments in the Soviet Union. If, as we hope, the present spirit will not lead to catastrophe, there is a chance that, sooner or later, the character of the Soviet regime may change for the better. We ought to invest some capital in this possibility."