PRESIDENT Reagan visualizes and promotes ``star wars'' exclusively in defensive terms. He tried repeatedly at Reykjavik to convince Mikhail Gorbachev that there is nothing threatening to others in the system, hence no reason for Mr. Gorbachev to object to it. Besides, Mr. Reagan promised to share the results of SDI research with everyone, including the Soviet Union. Mr. Gorbachev is not convinced and arms control is now hung up over SDI. Mr. Gorbachev has reasons.
First, if and when there are results from the Strategic Defense Initiative research, Ronald Reagan will long since have retired to his California ranch. Someone else will make the decision on sharing. The chances are negligible that any other American president would actually share the technology of SDI, particularly if that technology proved promising.
Second, Mr. Gorbachev cannot be sure that the technology of SDI will have only a defensive end product. At the present time, the American SDI research teams are working with the idea of using laser beams, particle beams, or the rail gun as the devices for knocking out hostile long-range missiles on their way. All three are said by the experts to be most useful outside Earth's atmosphere. Apparently they would be slowed and perhaps largely neutralized if used against a ground target.
A laser beam, however, can be reflected by a mirror. If it could be directed by a mirror against a missile in space, could it not also be directed by a mirror against ground targets? At present the experts are inclined to say probably not. But is Mr. Gorbachev in Moscow going to trust Western experts when he knows that the most enthusiastic advocates of SDI in the Reagan administration include the most passionate anti-Russians -- usually 'emigr'es from Eastern Europe -- who favor policies aimed at trying to bring down the present regime in the Soviet Union?
It is natural for Mr. Gorbachev to wonder why the politically active anti-Soviets in Washington are so eager for SDI if it does not have offensive as well as defensive possibilities.
Third, who knows what may emerge when the vast technological resources of the United States are concentrated on weaponry in space?
There is an important difference in the surroundings of arms control now from what they were when Americans and Soviets first began negotiating over SALT I, the first strategic-arms treaty.
At that time (1972) both Washington and Moscow assumed that Soviet research might go ahead faster than American. It was the era of Nikita Khrushchev's euphoria about the Soviet economy. It was roaring ahead. In those days Washington wanted tight curbs on Soviet research in space weaponry. The Soviets wanted maximum freedom to test.
The reverse condition prevails today. The Soviet economy has slowed down. Soviet technical research has slowed, along with the Soviet economy. US technology has surged ahead. Today the Americans want maximum freedom to test whatever may come out of the laboratory. Mr. Gorbachev wants to bottle space weapons in the laboratory.
At Reykjavik, the Soviets were arguing the case the Americans were pushing in 1972. The Americans were repeating the 1972 Soviet arguments. The change is the logical result of the fact that US technology is moving ahead faster than Soviet technology. The Soviets of today are afraid that Mr. Reagan's ``star wars'' dream may turn out to be only too real.
If it does turn out to be real, then the Soviets face the end of the era of ``equivalence'' built since their humiliation in the Cuban missile crisis of 1962. They may find themselves once more in a world in which the US may again, as it was in 1962, be the only true global military power -- which is precisely what the ``new conservatives'' in the Reagan entourage have always openly urged and pushed toward.
In effect, Mr. Gorbachev is asking Mr. Reagan to agree to maintain military ``equivalence'' indefinitely while Mr. Reagan is reaching for freedom to push ahead.
It is small wonder that no agreement was possible at Reykjavik. The central question left over from that meeting is whether the US is willing to mark time for 10 years, or reach for possible military superiority over the Soviets.