The goal that presidential adviser Paul Nitze has set for the new Soviet-American arms control talks is to enhance rather than imperil stability. The goal that President Reagan has set for his new Strategic Defense Initiative (SDI or ``star wars'') is to render nuclear weapons ``impotent and obsolete.''
The investigation of just how far these two goals are compatible prescribes the agenda for the most ambitious arms control talks ever attempted. To be sure, there are other issues in the talks: ordinary intercontinental missiles and intermediate-range missiles. But ``star wars'' remains the nub of the problem.
To an extraordinary degree for what is still only a drawing-board project (with current funding scarcely exceeding the levels that related research would have had even if Mr. Reagan had never called for SDI), ``star wars'' has come to dominate the nuclear debate.
It has brought the Soviets back to the negotiating table -- with the clear aim of stopping the program. It is prodding a rather alarmed Western Europe toward greater European security coordination in an attempt to present a united front to the United States as well as the Soviet Union. It is being hailed in the US as either a panacea or a catastrophe.
It will transform superpower negotiation -- if the US lead is followed -- from old-fashioned horse-trading to an unprecedented fundamental consideration of what nuclear conditions actually constitute stability and promote peace.
As Secretary of State George Shultz put it after meeting Soviet Foreign Minister Andrei Gromyko in January to set up these negotiations, the US is inviting the Soviet Union to join in a ``philosophical'' exploration of whether there could be a radical shift of deterrence from an offensive to a defensive basis. Mr. Shultz specified that SDI is just a research program designed to answer this question -- not a hard and fast commitment to development and deployment.
Similarly, Nitze has stressed that SDI, if it is to enhance stability and be worth deploying, must meet tough criteria of survivability and ``cost effectiveness.'' That is, it must be cheaper to deploy antimissile weapons than to multiply ways of countering them. Otherwise it will only trigger an open-ended arms race in space.
It is still too early to see how well or poorly SDI would pass Nitze's test. But it is clear that the results would differ depending on just what sort of antimissile defense might be erected. An ``astrodome'' that would provide 100 percent defense for both superpowers -- assuming they survived a decade of transition from an offensive to a defensive balance -- would strengthen superpower stability.
But by neutralizing superpower nuclear weapons, it could also -- in the great fear of the Europeans -- leave Western Europe at the mercy of Soviet-bloc conventional superiority on the Continent. Such a development would assure the security of a fortress America but could hardly assure the stability of Europe.
Alternatively, an American astrodome defense that the Soviets could not replicate has seemed to be the goal of some of the original SDI enthusiasts. Such a development would clearly reestablish the US nuclear superiority of the 1950s and '60s and enable Washington to dictate security terms to the rest of the world.
Neither outcome seems probable at this stage. An exclusive comprehensive defense of the US can be ruled out categorically. Although America has consistently taken the technological lead in the nuclear age, the Soviet Union has consistently imitated within five or six years whatever the US has pioneered.
That would not be long enough for the US to erect its astrodome defense, according to the projections of Nitze and others. And if it were attempted, it would give Moscow a highly dangerous incentive to force a nuclear showdown before it fell into decisive inferiority and lost its superpower status.
Nor does an astrodome defense for both the US and the Soviet Union seem all that likely, given the formidable technological hurdles.
According to Nitze's test of survivability and cost effectiveness, whatever components were deployed in space (in what has until now been deemed a sitting-duck regular orbit) would have to be defendable -- by some technology that would not simultaneously defend the more elusive missiles the SDI space components would be targeting.
And according to a study just published by Georgetown University's hard-nosed Center for Strategic and International Studies, ``A ballistic-missile defense that could protect American and allied populations with tolerably low leak rates does not now appear to be a realistic possibility.''
If no comprehensive defense of populations is feasible through disabling, say, 90 to 100 percent of incoming warheads, then two realistic possibilities are left -- as Reagan administration officials have been implying with increasing frequency. The US could knowingly deploy an antimissile defense that was only partially effective -- not for impossible military protection of cities, but for a political display of toughness toward the Soviets. Or it could aim at some kind of SDI that would protect weapons but not populations.
Traditional Western hard-liners would welcome the first course. Traditional advocates of arms control strenuously oppose it as profoundly destabilizing -- inducing exactly the wrong kind of confrontational response in the xenophobic Kremlin leadership without bestowing any compensating military advantage to the West.
The battle lines have not yet been drawn up on the second option, the ``point defense'' of offensive missiles that will become possible in the 1990s. This would probably entail superhardening of one's own missile silos or perhaps mobility of missiles, combined with emplacement of localized antimissile missiles and perhaps some very limited antimissile lasers or mirrors in space. The key antimissile missiles could be deployed, of course, only in contravention of the existing Anti-Ballistic Missile Treaty or after a renunciation or revision of it.
Such a development, contend proponents of such a point defense, could conceivably go a long way toward allaying the mutual fears that have sprung up in the 1980s about the adversary's capability and incentive for a first strike.
Ironically, a move in this direction, far from restoring a classical pre-1945 defense as Reagan has been championing in promoting his SDI, would probably shore up the very balance of offensive terror that Reagan has been hoping to escape from. It would aim at restoring the eroded survivability of weapons of attack. It would reinstate the old MAD, or mutual assured destruction: The ultimate weapons would remain invulnerable, while populations would remain so utterly vulnerable that they would continue to be hostages against either side's initiating a suicidal nuclear war.
This reversion, if it worked, might well strengthen ``strategic stability'' once both superpowers had their point defenses in place. That is, it could reduce still more the likelihood that either superpower would press the nuclear button in a calculated attempt to defeat the adversary.
But would such a development also strengthen ``crisis stability''? That is, would it reduce the risk that in the heat of some confrontation the superpowers might slide into escalation to nuclear war out of hubris, despair, preemption, or some other miscalculation? Most critically, perhaps, would it strengthen ``crisis stability'' during the very difficult 10-to-15 year transition period that is foreseen by Nitze in getting from here to there?
More broadly, what SDI option would most contribute to stability and therefore to peace? How much American SDI is enough to show American determination but not so much as to stoke the very nuclear tension it is intended to avoid? Would Washington and Moscow now engage in a mutually constructive instead of a mutually destructive designing of the 21st century?
The answers to these questions rest with a reelected President Ronald Reagan, a very new General Secretary Mikhail Gorbachov, and the negotiating teams at Geneva.