Nation: THE ABM: A NUCLEAR WATERSHED

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it away in talks with the Russians? These are points that have never been satisfactorily answered, even by those who first promoted the Sentinel's anti-Chinese system. McNamara led with his chin when he acknowledged in 1967 that only "marginal grounds" supported the decision to authorize an ABM. That speech has been an arsenal of criticism for ABM opponents ever since.

An Extra Option

The fact is that Lyndon Johnson's decision, dutifully but reluctantly implemented by McNamara, was based at least as much on domestic political considerations as on international factors. Sentinel, wags said at the time, was really a defense against American Republicans, not Chinese Communists. Johnson might well have halted the Sentinel project last summer if he could have arranged, as the Soviets wished, to begin arms-control talks. He had on his desk an unsigned message confirming his willingness to negotiate on the night that Ambassador Anatoly Dobrynin brought him word of the Soviet invasion of Czechoslovakia. That was the end of that.

Many responsible scientists and strategists make a cogent case for Sentinel's deployment. Leon Johnson, a retired Air Force general and National Security Council aide, argues that an ABM gives the U.S. an extra option in any crisis. Its existence in a future confrontation, say with a bellicose nation that has a few primitive missiles, would allow the U.S. a third alternative other than acquiescing to blackmail or being forced to devastate the antagonist. The U.S. could employ conventional forces in a local situation, knowing that a small nuclear attack could be blunted.

Dr. Donald Brennan, a founder and former president of the Hudson Institute, a private research center, argues that even a flawed defense "makes an attack much more complicated and would tend to argue against anyone making one." He disagrees with the contention that it is cheaper and easier for the offense to stay ahead of the defense. Defensive technology has reached the point, Brennan maintains, where it requires equal effort for the offense to keep pace. To this, Simon Ramo, vice chairman of the billion-dollar-a-year TRW electronics company, replies that with "one-tenth of the budget of ABM, thick or thin, I could wreck the system."

Brennan and a number of other ABM advocates part company with the "thin" school. They urge a fuller deployment aimed squarely against a Russian attack. If both the U.S. and the Soviet Union could agree to emphasize their defensive posture, says Brennan, "we might find it very easy to agree on an effective ceiling on offensive forces."

Even some of the most energetic enemies of Sentinel deployment say that they would subscribe to a comprehensive ABM program, notwithstanding the cost, if only they could be persuaded that it would provide an impermeable shield. Says Physics Professor Alvin Saperstein of Wayne State University: "It is not a question of trusting the Russians or the Chinese. You can't trust them. But I don't trust our own military not to lead us to disaster either. If I felt the ABM were effective, I'd live with the damn thing in my back yard. But it isn't." Thus many who want Sentinel stopped favor continued exploration for technological breakthroughs that might assure a more reliable defense.

A crucial question for the