How is one to explain the passionate, sometimes almost frenetic, denunciation of the president's proposal for a defense against Soviet ballistic missiles? Even the label, "Star Wars," seems designed to denigrate, to conjure up a vision of Hollywood production, a matter for ridicule, not serious national debate. While the critics scoff, the public seems to appreciate the common-sense approach of seeking to defend ourselves. What, after all, is the sin of attempting to develop a defense against Soviet attack?

Let us acknowledge at the outset that there are aspects to the Strategic Defense Initiative (SDI) that warrant healthy skepticism. This research carries a costly price tag of $26 billion. However, by today's standards of $100 million bombers and $5 billion aircraft carriers, the SDI costs -- which are to be spread over more than five years -- are not unreasonable if the research effort produces results that will improve the nation's security and that of our allies. We think it can.

It is also a legitimate matter of concern that some of our allies are deeply opposed to SDI. As ones who have discussed the issue with some of our NATO partners, we are persuaded that there is much confusion and misunderstanding on their part. Past experience also suggests that these concerns may, in time, be allayed if our diplomacy is patient and skillful. Such would already appear to have been the case with Margaret Thatcher.

It is also true that the most extravagant expectations for SDI may never be fulfilled. It is not unreasonable to be skeptical about whether a perfect defense will ever be developed. The president's hope that SDI will help to make nuclear weapons disappear from the face of the earth is surely utopian. Still, these are not ignoble goals, and at this stage neither supporters nor critics of SDI can speak with confidence about what technology and diplomacy may accomplish decades hence.

One must probe more deeply to comprehend the antagonism toward the SDI that has emerged from certain quarters. When one does, two underlying issues emerge. They have to do with nuclear strategy and arms control.

While declaring their confidence that SDI won't work, the critics, in fact, are fearful it will. At least they fear it will work well enough to call into question their preferred nuclear strategy. Most critics adhere to the school of mutual assured destruction (MAD). That emerged in the 1960s from the mind of Robert McNamara, who was then secretary of defense and is now one of the principal critics of strategic defense. His calculations convinced him that so long as millions of Russians and millions of Americans were at risk of nuclear attacks on the cities on each side, each would be deterred.In this view defenses were bad because they removed the hostages that assured deterrence. There was then, and there is now, much wrong with this thesis.

Not the least of the problems is that the Soviets never bought McNamara's strategy. They don't believe in city busting as the prime objective of nuclear strategy. Thus, it is not clear that such a threat is the one most likely to deter them. Indeed, the Soviets, despite McNamara's contrary prediction, spent massively to overcome America's lead in offensive weaponry, going well beyond any conceivable inventory justified solely in terms of the requirements for the MAD strategy. In time, many U.S. leaders came to the realization that MAD did not serve us well either, and U.S. strategy has, for more than a decade, under Democratic and Republican administrations alike, been moving away from this concept.

Since the Soviets did not believe in the MAD strategy, they refused to rely solely on offensive nuclear capabilities and in addition deployed impressive defenses. They have more than 10,000 ground-to-air defensive missiles and thousands of fighter aircraft to protect against our bombers. We have none of the former and pitifully few of the latter. They have deployed ballistic missile defense in the Moscow area that provides defense to their central government and party apparatus and to two-thirds of the heavily industrialized western U.S.S.R. They have an impressive civil defense system, which has concentrated on defending key government and industrial people. They have continued to harden and make mobile their ballistic missiles and command centers.

As Defense Secretary Caspar Weinberger recently pointed out, thay have spent more on strategic defense than on strategic offense since the signing of the ABM Treaty. This is hardly consistent with the MAD strategy or with the thesis of those Americans who decry deployment of defenses as inconsistent with their unrealistic belief that the Soviets are willing to adopt a MAD strategy.

In fact, the Soviets built their forces to support the strategy they have held to consistently, based not on targeting U.S. cities but the U.S. military establishment. As a result, they are today capable in a first strike (and their doctrine has always emphasized the importance of surprise) of reducing the U.S. retaliatory force to a relatively small fraction of its nominal strength. Thus, we could be left with a force that, while having some countermilitary capability, was most suitable for attacking Soviet cities, even though our own cities had not yet been attacked by the Soviets -- an unenviable choice for any president. Under the circumstances, we might find our strategy, having failed to deter, would leave him with unbelievably stark alternatives: suicide or surrender. Even if such a foreboding scenario seems unlikely, its prospect casts dark shadows that can influence peacetime and crisis actions well short of nuclear war.

Why is it not a good idea to seek alternatives that avoid such a stark choice? Is it not worth a considerable effort to see whether some degree of defense might help ensure deterrence? If deterrence could fail, why shouldn't we try to protect ourselves as best we can? Must we accept for all time a strategy based on the threat of killing millions of innocent men, women and children -- a strategy that Catholic bishops have rightly denounced as immoral? The critics of SDI have no good answers.

The opponents of SDI have a second worry. They fear it would complicate arms control negotiations with the Soviets. One might have thought that the barren results of the past two decades of arms control negotiations would have given rise to second thoughts to those who would have us rely so heavily on them for our security. They are most concerned about protecting the "jewel in the crown" of arms control, the ABM Treaty of 1972.

When the treaty was signed, the United States dismantled its one system and sharply cut back on research and development, even though these were permitted. The Soviets have proceeded to complete a nationwide radar net; to complete deployment of the one permitted system; to create a production base that would permit rapid expansion of conventional but advanced ABM capabilities; and to conduct extensive research in precisely those advanced technologies that would be encompassed by the SDI program. They have fully exploited the possibilities permitted by the treaty while we have not, and most observers are satisfied they have actually violated the treaty limits, most notably in deploying a large radar at Krasnoyarsk.

Apologists for the treaty hesitate to acknowledge these realities. The Soviets, being realists, are unlikely to permit any arms control agreement to stand in the way of advancing Soviet interests, in most cases at the direct expense of the West. Indeed, the Soviets' recent initiative to draw the Reagan administration into new arms control discussions clearly appears to be based upon a desire to kill off SDI while leaving them as free a hand as possible to pursue their own ballistic missile defense and antisatellite efforts. Any objective review of arms control history will demonstrate this to be vintage Soviet arms control strategy.

Still, critics of SDI hang fast to the belief that they can talk the Soviets into adopting a mutually suicidal strategy, while engaging in arms control efforts that, to succeed, would require the Soviets to abandon not merely some weaponry of which they may be fond, but their most fundamental political objectives. For Soviet exploitation of military power -- the one thing the Soviets are good at developing -- is not just some minor aberration in otherwise reasonable behavior. The Soviets develop that power because they require it for purposes of political intimidation and, should that fail, for actual employment, as they pursue their goal of a world pliant to Soviet views.

Under these circumstances, it is folly for us to place our security solely or even primarily on arms control. The notion that the Soviets through arms control negotiations are likely to abandon hard-won military advantages over the West is about as naive as was the 1960s prediction that they would not even try to match our nuclear capabilities.

As we have suggested, the current defense debate is not just about the president's Strategic Defense Initiative. It is about more fundamental issues: How can we best prevent nuclear war? How ought we to deal with the Soviet Union in a continuing adversarial relationship? How do U.S. nuclear strategy and arms control concepts fit into and support nuclear war deterrence and prevent the expansion of Soviet influence?

No one side in our internal debates has a monopoly on wisdom, and one wishes the critics of the president's SDI program would cease acting as if they did. Would it not be reasonable to see whether this research effort can come up with capabilities that may promise the West a safer, more promising future than total reliance on the threat of mutual destruction?

Even though the research may be only partially successful, as Weinberger has recently suggested, if we can develop and deploy defensive systems with capabilities more modest than a perfect defense, might that not be very valuable in strengthening deterrence? Even if defenses initially provided protection of valuable military assets such as land based ICBMs, bombers and command-and-control centers, might that not be preferable to proliferating generation after generation of new offensive weapons systems? Even if an imperfect defense could save "only" tens of millions of lives, is there not some merit in such a defense?

Finally, if we are successful in developing increasingly capable defenses against Soviet nuclear attack, might not this induce the Soviets to adopt a more forthcoming position on arms control? We cannot with confidence answer these questions positively. The prospects are not without merit, however, and it is to these issues that the 1985 defense debate should turn if it is to contribute to making the nation and its allies more secure.