STRATEGIC QUESTIONS

By Evan Thomas.

To Ronald Reagan, the mutual suicide pact that has precariously preserved the nuclear peace for the past quarter-century is unacceptable, indeed immoral. Why not, he asked in his famous Star Wars speech, switch from a policy of mutual assured destruction (MAD) to one of mutual assured survival by creating a defensive shield that would ''render nuclear weapons obsolete''? Although that dream might seem unassailable, the strategic realities involved raise a far more unsettling question: Will the attempt to create a nuclear shield enhance stability or undermine it? In attempting to rid the planet of doomsday weapons, might SDI merely increase the risk of their use? At the TIME conference on SDI, it was apparent that there was a deep division within the Administration over the real aim of SDI. While he applauded Reagan's ''vision,'' Assistant Secretary of Defense Richard Perle bluntly stated that a leakproof Astrodome against missiles ''is not a short- term proposition, and it may not even be possible in the long term.'' Gerold Yonas, the chief scientist for SDI, was equally emphatic. ''The idea that we are going to protect all the people somehow with a perfect defense'' is the ''wrong approach.'' Instead, he argued, the goal is to make the Kremlin unsure that it could launch a strike that would knock out America's capacity to retaliate. The immediate goal of SDI, Perle agreed, is ''not the defense of the nation as a whole, not of every city and person in it, but the defense of America's capacity to retaliate.'' Thus he saw a more realistic mission for a space-based defense system: guarding ''our critical defense installations, ballistic missiles, command and control facilities.'' He added that ''a 50% effective defense could make a significant and I think vital stabilizing contribution.'' Later at the conference, when Arms-Control Adviser Paul Nitze was informed of Perle's statements, he expressed surprise. ''I know for a fact,'' said Nitze, ''that it is contrary to the White House view of the matter. Maybe it's his view, but I can't understand the rationale for it.'' The rationale, according to those who advocate a system to protect silos, is that they are now vulnerable to a pre-emptive attack by the Soviets' vast arsenal of fast, accurate warheads. At the conference, Walter Slocombe, who during the Carter Administration held a Pentagon post comparable to the one now occupied by Perle, agreed that ''in principle'' defending silos is ''not a bad idea.'' But, he argued, there are cheaper and more reliable ways to defend the U.S. capability to retaliate. Among those suggested at the conference: hardening missile silos and developing a system of mobile missiles that would be less vulnerable to attack. If protecting silos is the real aim of SDI, asked Stanford Physicist Sidney Drell, why has the Administration dropped all funding for the one defensive system now known to be an effective terminal defense: nuclear-tipped interceptor missiles? Though he personally does not favor an active missile defense, Drell questioned the logic of diverting money from available off-the-shelf technology and using it to chase Reagan's dream of a multilayered shield against all Soviet missiles. Protecting specific targets, be they cities or silos, is not a new idea. Every President from Eisenhower to Nixon considered some kind of terminal defense, said M.I.T. Engineering Professor Jack Ruina, who began advising on nuclear strategy during the Eisenhower Administration. Yet each of those Presidents was ultimately bedeviled by a stark truth about nuclear weapons: it has always been cheaper to build offensive weapons than defenses to stop them. Earlier Presidents, asserted Ruina, realized that by building defenses, they would just invite the Soviets to build more and different types of offenses, thus igniting a destabilizing new round in the arms race. Even if the presidential dream of a perfect defense against Soviet ICBMs could be erected, it would not stop the Soviets from using other offensive weapons, such as bombers and low-flying cruise missiles. Yonas acknowledged that defending against cruise missiles is ''really not part of SDI.'' To stop a bomber or cruise-missile attack would require an extremely costly air- defense system. Even then, an enemy could no doubt find ways to transport a devastating nuclear bomb to the U.S. While acknowledging the risk of an intensified offense-defense spiral, Perle speculated that the Soviets might not even try to overwhelm a partly effective shield against ballistic missiles. ''It just may be,'' he said, ''that the development of a defense would discourage the Soviets from making the very sizable investments necessary to overcome that defense.'' This was a curiously optimistic view from a hard-liner who in the past has always assumed the worst about Soviet intentions. Nitze, on the other hand, argued that the U.S. cannot afford to hope that the Soviets will in effect say ''uncle.'' Nitze stressed, as he has on earlier occasions, that the U.S. should not deploy SDI unless it is ''survivable.'' It cannot be so vulnerable that the Soviets would be tempted to shoot it down. And it must be ''cost-effective at the margin.'' This means that once SDI is deployed, it must not be cheaper for the Soviets to add new offensive weapons than it is for the U.S. to add new defenses to stop them. This standard has met some resistance from the chief of the SDI program, Air Force Lieut. General James Abrahamson. In testimony before Congress two months ago, Abrahamson argued that SDI should be ''affordable,'' a more elastic definition. Nitze, a shrewd bureaucratic infighter, persuaded the President to sign a national security decision directive making his criterion official policy. Asked at the TIME conference whether he was trying to skirt Nitze's standard, Abrahamson demurred. He conceded that he might have ''erred'' by using the word ''affordable,'' but he seemed to fudge by insisting that the question was not merely economic. ''You also have to consider the military situation and what the danger is that the nation faces.'' Defense Secretary Caspar Weinberger, in an interview with TIME last week, was more explicit in challenging Nitze's standard. ''I think the technical definition of cost- effectiveness, somebody trying to define what the margin means, is not very useful,'' he declared. ''We can afford to do what we have to do. My own feeling is that we should do SDI if it is in any way technically feasible.'' Star Wars has become so controversial in the academic community that hundreds of scientists have signed petitions saying they refuse to work on the program. This rather short-sighted view was not shared even by the critics of SDI at the TIME conference. They agreed that research should continue, both to match Soviet efforts and to preserve the remote possibility that someone someday might discover a technology that diminishes the inherent advantage of offense. Building effective nuclear defenses, the conferees acknowledged, is as much a political challenge as it is a technological one. The shift from ''offense-dominated'' deterrence to ''defense-dominated'' deterrence, in the argot of the experts, must be accompanied by arms control. ''The path to a safer world,'' argued Drell, ''is going to be paved largely by the negotiating process, not by another laser.''

For more than a decade, a rickety arms-control structure has attempted to keep a lid on the offense-defense spiral. The ABM agreement in the 1972 SALT I talks curtailed missile defenses, while an interim treaty that year and the SALT II talks of 1979 limited offensive weapons. In the view of Administration hawks, however, arms control has been a failure. Because they felt they could not compete with the U.S. in building missile defenses, Perle said, the Soviets agreed to the ABM treaty and ''cleverly negotiated a halt on our side while intensifying their own effort.'' The Soviets have now ''reversed the relative capacity of the two countries to deploy a defense,'' he charged. Defense Department hard-liners led by Weinberger and Perle are pressing to scuttle the existing arms-control framework by abandoning SALT II and adopting a revisionist interpretation of the ABM treaty. In its Article V, the ABM pact forbids development, testing and deployment of any new ABM system --land-based, sea-based or space-based. But Perle has focused on another provision of the treaty, the so-called Agreed Statement D, which declares that defenses based on ''other physical principles'' undreamed of by the 1972 negotiators would be ''subject to discussion.'' The negotiating record, according to Perle, shows that the Soviets repeatedly asked, ''How can you ban phenomena you haven't discovered yet?'' The ABM treaty, he thus argues, is no impediment to forging ahead with Star Wars. Nitze, who helped negotiate the 1972 ABM treaty, said he believes this expanded interpretation of the ABM agreement is ''correct.'' Nevertheless, he reaffirmed that the Administration's policy is to stick to the hitherto accepted interpretation of the ABM treaty, which would restrict Star Wars development. Of Perle's statement earlier in the day that the U.S. would adopt the looser ABM interpretation during ''the lifetime of this Administration'' in order to proceed with testing SDI, Nitze responded, ''I think there is no doubt but that that is the view of Mr. Weinberger and Mr. Perle, but it is certainly not my view, and I do not believe it to have been so decided by the President.'' Nitze, who decried the Soviets' superiority in heavy land-based missiles as ''a road to disaster,'' did insist that the U.S. ''cannot accept'' the Soviets' demand that the U.S. halt ''substantive'' work on SDI. Yet he hinted that SDI could be an important chip to use in a bargain that would trade limits on offensive weapons for limits on defensive ones. His language in his speech to the conference was carefully hedged, but its implications were intriguing. ''Were the Soviets to work with us in a meaningful exploration of significant reductions'' in offensive weapons, he stated, ''we could examine how the level of defense would logically be affected by the nature and level of offensive arms.'' ''I'd be interested myself in talking to them about that kind of trade,'' Nitze stated at a question-and-answer session. Asked if the President would share his interest, Nitze answered, ''I honestly believe that the President is in fact very much interested in working out a deal'' if it was ''consistent with the security interests of the U.S.'' and part of a ''general move toward a stable relationship between the two sides.'' What the President does not want, said Nitze, ''is a bad agreement with the U.S.S.R.'' Persuading both the Soviets and Reagan to make the concessions that would be necessary to strike such a grand compromise will be difficult. Just as difficult, perhaps, as developing the technology required to make Star Wars a reality. On this essential point, Drell gave Albert Einstein the last word: ''Politics is much harder than physics.'' BOX: The Principal Speakers At TIME's SDI Conference: LIEUT. GENERAL JAMES ABRAHAMSON, director, Organization ASHTON CARTER, associate professor of public policy, Kennedy School of Government, Harvard; editor, International Security SIDNEY DRELL, deputy director, Stanford Linear Accelerator Center STEPHEN MEYER, associate professor of political science, M.I.T.; consultant, Defense Advanced Research Projects Agency PAUL NITZE, Special Adviser to the President and the Secretary of State on arms control RICHARD PERLE, Assistant Secretary of Defense for International Security Policy JACK RUINA, professor of electrical engineering, M.I.T.; former director of the Advanced Research Projects Agency WALTER SLOCOMBE, former Defense Department official and director of the Task Force during the Carter Administration GEROLD YONAS, chief scientist, Organization

With reporting by Bruce van Voorst/Washington