The most revealing thing about the argument against the MX Dense Pack is its implicit assumption that the Soviets, our partners in arms control for more than a decade, will respond to it with new, costly and uncertain weapons and tactics to assure their capacity to destroy 100 U.S. missiles in their hardened shelters. That liberal lawmakers should now arrive at the conviction that the Soviets will go out of their way to destroy our land-based deterrent, by whatever means and at whatever cost may be required, is too richly ironic to pass without comment.

Not with a whimper but a bang has the debate over Dense Pack thus ended the 20-year controversy about Soviet strategic objectives. In their enthusiasm to regale the Congress with the several ways in which MX might be destroyed -- earth-penetrating warheads, attacks timed to within milliontha of seconds, "pindown" attacks, and the like -- legislators and scientists who for years have dismissed the idea of a Soviet attack on our land-based force as an obsessive delusion of worst-case defense planners, have now gone them one better: they not only imply that the Soviets can destroy our aging Minuteman missiles; they can be counted upon to invest billions in new methods of destroying MX as well.

We have come a very long way indeed in the 20 years since the defense secretary, Robert S. McNamara, believed that for the Soviets to counter President Kennedy's Minuteman missile was so technically and financially demanding that they wouldn't even try. Throughout the 1960s and 1970s, as the Soviets deployed a succession of new missiles, each more powerful and accurate than its predecessor, the central strategic debate turned not on whether our missiles should be placd close together or far apart, but on what to make of the Soviet buildup and how to respond to it.

On one side of that central strategic debate were the opponents of most U.S. strategic initiatives--ABM, multiple warheads, improved accuracy, the B1 and the rest. Like Sens. Kennedy and Hatfield or officials like Paul Warncke and Herbert Scoville, they disputed any suggestion that the Soviets might be seeking a capability to strike and thereby disarm the United States. Believing that deterrence was inherently stable, that the United States possessed vastly more weapons than needed, that the Soviets sought only parity and not superiority, they displayed extraordinary inventiveness in explaining Soviet behavior as benign. Thus the buildup of Soviet nuclear forces was an example of mindless imitation or bureaucratic inertia dissociated from any strategic concept. Soviet weapons were bigger and more powerful, they said, because they were incapable of making them smaller and more accurate. They accepted and defended the notion that the Soviets shared our concept of deterrence and, like us, eschewed acquisition of a first-strike capability. In all of this they felt fortified by the technical judgment that a first strike, even with superior forces, was too risky and uncertain for any rational Soviet leader seriously to consider.

On the other side were the proponents of an ongoing modernization and adjustment of the U.S. strategic force -- senators like Scoop Jackson and John Tower, strategists like James Schlesinger and Albert Wohlstetter, who believe that stable deterrence requires periodically fixing those vulnerabilities in our strategic forces that are an inevitable result of their age and the Soviet offensive buildup. Unwilling to disregard the expanding Soviet offense or to dismiss the risk that they might indeed desire the capability to destroy our deterrent, they have sought to assure that our triad of land-, air- and sea-based forces would survive even a determined Soviet program to render them vulnerable.

Throughout the debate, the technical details of the weapons systems involved, while important for the experts, have never been decisive. But especially in recent years, in the face of a massive Soviet buildup acknowledged by Democratic and Republican administrations alike, the opponents of strategic modernization have found "it won't work" more effective than "it isn't necessary" in gathering votes against specific systems.

But in arguing that Dense Pack won't work because the Soviets will surely devise ways to defeat it, they not only align themselves with the Team B finding that the Soviets are seeking superiority, they are abandoning the wellspring of their own complacency -- the notion that uncertainty is the key to strategic stability.

Whatever happened to the familiar litany, popularized by a collection of committees, coalitions and congressmen, that the Soviets would never strike our Minuteman missiles with their untested offense because they could never be certain that the attack would succeed. Now they are to be found caucused around a new line: that with MX in the Dense Pack deployment we could never be certain that a Soviet attack would fail. Why is it that scientists who for years have urged restrictions on the flight testing of ballistic missiles, on the theory that the resulting uncertainty about their performance would strengthen deterrence, now prefer the certain vulnerability of Minuteman to the much greater uncertainty the Soviets would face in challenging Dense Pack.

Out of all this one point emerges with crystal clarity: every argument that "MX won't work" drives more powerfully to the conclusion that MX, or something like it, is necessary.

The growth of technically sophisticated Soviet forces has been such that for the future we will have to compose a strategic deterrent from a mulitiplicity of partial solutions, none of them perfect, all of them vulnerable to some level of attack under some circumstances. The days when our lead in trechnology enabled us to deploy strategic systems that could remain invulnerable for long periods, with little more than routine maintenance, are gone forever. Persisting in the search for the perfect single system will drive us to unacceptably high budgets chasing hopelessly unrealistic goals.

In the more than 30 years since the first elements of an American deterrent were designed, every president and every secretary of defense has concluded that our security requires a survivable land-based missile. As we move toward a national decision, those who argue that we can do better than Dense Pack, or that there is a solution more effective than the deployment of MX, will have the chance -- and indeed the obligation--to develop their ideas and promote their alternatives.