Walter Pincus' recent article, "The Soviet Strategic 'Advantage,'" [op-ed, Feb. 5] raises several points with which I would like to take issue.

Let me first make some factual corrections. The Soviet Union does not have 100 SS18s deployed, but almost 200. Moreover, the Soviets have only recently perfected the SS18 MIRV program and can be expected to deploy the 308 (and possibly 326) SS18s -- each with 10 warheads -- as permitted under the terms of SALT II.

The fourth generation Soviet ICBM forces (the SS17, SS18, SS19) are capable of achieving, and have virtually achieved, the missile accuracy of the U.S Minuteman III force with the INS-20 guidance system -- an accuracy on the order of.1 nautical miles. Thus, under the terms of SALT II, the Soviets will be able to deploy over 6,000 MIRVed ICBM warheads, with each warhead having the capability to destroy one of the slightly more than 1,000 U.S. ICBM silos, and the other two or three hundred U.S. military targets (including bomber fields and submarine facilities) that the Soviets might want to attack. The Soviets would also retain a significant post-attack superiority. The United States has no similar capability.

The emergence of this Soviet capability is contrary to what is called "crisis stability" -- that is, we should not threaten or have threatened a large portion of our strategic force which could be destroyed in a surprise attack. We also do not want to be placed in a position where the survival of our ICBMs is dependent on launching them from under attack (and we would not necessarily have two hours, as alleged by Mr. Pincus, to make that decision -- 20 minutes is much more likely). Such a response would lead to an all-out spasm nuclear war and we would lose not six million American lives, but 100 million. We thus want to be able to control the escalation of any nuclear conflict and terminate any possible hostilities at the lowest threshold level possible. Whether this is possible we don't know, but we must retain that option, given the alternative.

It is true that the United States, after absorbing a surprise Soviet attack, would still retain a significant capability in surviving submarines and bombers and cruise missiles. But our bombers and cruise missiles would still be subject to penetration problems, while our submarines would be limited to attacking so-called Soviet "countervalue" (economic) targets. Such a response would inevitably lead to a Soviet response in kind. Would we dare risk such an attack in the face of over-whelming Soviet strategic superiority; would such a U.S. capability provide sufficiently a deterrent to prevent an attack on U.S. forces from occurring; should we be limited in a response capability that would lead to an all-out nuclear war? Our present policy guidance says we should not be so limited.

In this context, let me also point out that contrary to the "assured destruction" myth, the recent PDM18 directed studies on nuclear-weapons targeting illustrate very clearly that the retaliatory capability of the United States could not significantly retard or prolong the reconstitution of the Soviet economic structure, let alone destroy Soviet society.

The primary purpose of our nuclear forces is, of course, to provide deterrence and a stable strategic environment. Until the latter part of the last decade we never really had to focus on what constitutes deterrence because we had substantial superiority. The year 1979, however, represents a turning point.

As revealed in the current Department of Defense posture statement, the strategic capabilities of the Soviet Union have begun to surpass those of the United States, and this Soviet advantage will grow through much of the 1980s.

Mr. Pincus is correct that the United States has options to redress the growing strategic imbalance and restore stability. That is the purpose of the so-called Multiple Aim Point (MAP) ICBM basing system -- a proliferation of vertical shelters wherein U.S. ICBMs would be randomly moved around. A MAP basing system would restore stability because for the Soviets to successfully destroy U.S. ICBMs, they would have to attack all of the shelters. They would then be forced to expend more warheads than they would destroy, thus theoretically ending up in a post-attack inferior position. Such a situation would be stable because it would reduce any incentive to strike first.

It is clear that despite what political benefits SALT II may or may not entail, the agreement in and of itself will not enhance stability. U.S. strategic programs will be necessary to do that. The prospective SALT II agreement, in my view, has several serious deficiencies; but what concerns me most is that the agreement is advanced as obviating the need for U.S. strategic programs that are necessary to maintain a U.S. Soviet strategic balance and stability.

Finally, on the issue of whether U.S. restraint has been matched by the Soviets, I think it is important to note Defense Secretary Harold Brown's comment on that subject:

"What concerns me most about the continuing Soviet military buildup is its persistence and how that continues regardless of what the United States does.... We build up our forces, they build up theirs. We reduce our forces, they build up theirs... if the present trends continue for another five years, I believe the relative military positions [of Russia and the United States] would be a cause of real difficulty for the United States."

That, in my view, sums up very adequately the situation we face today as a nation. But I believe there is hope. The Soviet leadership is composed of rational, cautious men. If we show them we are serious, we will contribute substantially to a peaceful and stable geopolitical environment.