Hitting a fly in space. Time to ground Reagan's dream of SDI

AS the end of his presidency approaches, Ronald Reagan still dreams of ``star wars.'' He claims it will forever ``render nuclear weapons impotent and obsolete.'' Once our missile shield is in place over the United States, he wants to offer the technology to the Soviets, so they can reproduce it. Ironically, as long as the US seeks star wars (the Strategic Defense Initiative), our lives will be that much more endangered. As a nuclear physicist, I have devoted the major portion of my scientific efforts in the last few decades to the study of arms control, especially its technical problems. I feel qualified to judge the star wars program on its merits (or rather, lack thereof).

But it does not take much technical sophistication to recognize the fallacies of star wars. Our space defense would have to be 100 percent impenetrable. If it were any less effective, we would risk millions of casualties.

If either side starts to deploy a ballistic missile defense system, the other will likely react in two ways: First, to build more offensive missiles to guarantee that it could still retaliate. The other side is also likely to seek loopholes in star wars defenses, then invent new and more dangerous missiles to circumvent it. Second, it would start to emulate the ballistic missile defense of the side deploying it. These reactions would precipitate a new and destabilizing technological arms race.

The situation now strongly resembles the one in the late 1950s. The Soviets were then prepared to embark on an extensive deployment of antiballistic missiles. Premier Nikita Khrushchev boasted that his scientists had perfected an antiballistic missile (ABM) system capable of hitting a fly in space.

He was not, however, asked how the system would work if it had simultaneously to contend with a hundred flies or with a thousand objects that resembled flies, of which 100 were real flies and the rest were just decoys.

The Soviet scientists at first believed that because the ABM system was defensive, it posed no threat and was therefore good. We American scientists met with them regularly at the Pugwash conferences in Nova Scotia. We argued the destabilizing properties of ABMs. They quickly saw the point, joining with us to persuade our governments to make a treaty to limit ABMs.

Our two governments later concluded such a treaty. Without it, the number of missiles could have increased astronomically to overwhelm defenses, and the arms race might have gone haywire.

The current arguments about the dangers of deployment of space-based defenses parallel those of the ABM debate - except that the US and the Soviet Union have reversed positions.

Because star wars encourages the development of new and more dangerous weapons, we must stop it and expose its fallacies. Only then can we move away from this pipe dream of a defensive cocoon and toward disarmament.

Bernard Feld is a professor of physics at the Massachusetts Institute of Technology and a board member of the Council for a Livable World. He chaired the Committee on Pugwash conferences of the American Academy of Arts and Sciences.