Why Keep `Star Wars'?

RONALD REAGAN liked to say his Strategic Defense Initiative could make nuclear weapons ``impotent and obsolete.'' That's impossible, at least technologically. As long as such weapons can be bolted to rockets or placed in artillery rounds or dropped from airplanes or even tucked into backpacks, the possibility of nuclear war exists. There is no umbrella defense through ``star wars'' or any other military means. But does this mean that SDI is a dead item? That the Bush administration and the 101st Congress should shut it down and redirect its billions of dollars to offensive military forces or reducing the deficit? No, and there are several reasons for this:

First, the kinds of things now under the aegis of SDI were being investigated before Mr. Reagan's startling star-wars speech six years ago - use of directed energy (lasers and particle beams) for military purposes, high-speed intercepts in space, ability to discriminate quickly among thousands of potential targets, computers to handle complicated ``battle management'' involving millions of bits of information. Unfortunately, as long as there are mistrust and conflict between nations and as long as scientific progress continues, the military use of space has to be considered.

Second, the Soviet Union - for all its tut-tutting on SDI - has a pretty fair strategic defense setup itself: mobile radars, interceptor rockets able to defend against warheads as well as aircraft, large phased-array radars, and antisatellite weapons. It spends a lot on directed energy, and it has the only missile defense system deployed under the Antiballistic Missile Treaty. As a hedge against a Soviet breakout in strategic defense, the United States at least needs to know as much as possible about the subject.

And third, the US now has more than the Soviet Union to worry about. CIA director William Webster warns that at least 15 third-world countries will be able to produce ballistic missiles by the year 2000, and congressional investigators say there could be 33 nuclear powers by then. India (which has not signed the Nuclear Non-Proliferation Treaty) is about to test a new missile with a 1,500-mile range.

So the world is a complicated place, and the arms race in space has already begun. So what should President Bush and Congress do about star wars?

They should continue funding missile defense research at between $2 billion and $3 billion a year. That's about 1 percent of the Pentagon budget, at most, and only about half of what Reagan wanted for SDI in the next fiscal year. But it's still plenty to keep the scientists hard at it.

They should not press for early deployment of space-based warhead interceptors, as some star-wars enthusiasts are urging. This would definitely escalate the arms race in space. They should, however, explore Sen. Sam Nunn's proposal for a ground-based ``accidental launch protection system'' that could be of interest to the Soviets as well.

The arms race in space really began with the first spy satellite. The challenge now is to control that race in a way that provides true national security.