DURING the United States-Soviet arms control talks beginning this month in Geneva, one sure topic will be the Soviet phased-array radar at Krasnoyarsk. The US has already accused the Soviets of violating the Antiballistic Missile Treaty by building this radar. Its location and orientation are in clear violation of the treaty. Soviet protestations that the radar's purpose is space tracking are not supported by that orientation: It is ideal for plugging the last gap in Soviet early warning radar coverage and is not very useful for tracking satellites. What is the real purpose of this radar? And why have the Soviets apparently decided to violate the treaty in such a deliberate and obvious way? The answer to the first question may enlighten us as to the second.
The radar may be intended to protect at least some of the Soviet land-based ICBMs against a US first strike.
The Soviets rely heavily upon their land-based missiles, which carry about 75 percent of their strategic arsenal. The remainder is located primarily on submarines, which are active only 10 to 15 percent of the time. (In contrast, the US has most of its warheads on bombers and submarines, and each US sub is on duty about 50 per- cent of the time. If the USSR were to lose all land-based missiles in an attack, its strategic arsenal could be reduced from about 8,000 warheads to as few as 150 to 250, with up to 300 more in the unlikely event that much of the Soviet bomber fleet survived.
It is worth nothing that the Reagan administration's concerns abut the now-discredited ``window of vulnerability'' arose from fears that a Soviet first strike would leave us with only 2,800 (not 250!) warheads for retaliation. One should consider how insecure the historically paranoid Soviets might feel about facing a far worse scenario.
Perhaps not coincidentally, the Krasnoyarsk radar will be completed not long before the initial deployment of upgraded Trident D-5 missiles on our submarines. These missiles will, for the first time, permit the US to destroy a very large fraction of the Soviet land-based missile force. What's more, their invulnerability renders the Tridents immune to Soviet preemption.
The accuracy of the D-5s will be comparable to or better than that of our land-based Minuteman III missiles. With an overall performance level which is optimistic but nevertheless within the range that Soviet planners must consider, the fully deployed Trident fleet and the existing Minuteman III force could, together, destroy over 95 percent of the Soviet land-based missiles.
To deter a first strike, to assure their national survival, the Soviets must be able to assure the survival of a significant fraction of their missiles -- just as we must. Although the Krasnoyarsk radar alone is not sufficient for missile defense, such a radar would be the one item that must be started many years in advance. Interceptors and ancillary radars, which would also be needed for a missile defense system, could be added later.
Although the radar is vulnerable to attack in the first stages of a nuclear exchange, it is well set back from the Soviet borders (in violation of the treaty). The radar and associated components might survive long enough to protect a significant number of those ICBMs, although they could not protect cities. Even if the radar is not developed into a full defense, it might provide enough warning to allow Soviet missiles to be launched before US warheads arrive.
One can imagine a scenario in which the Soviets halt construction a few months before completion and then use the radar as a bargaining chip in negotiations with the US. They could threaten a rapid breakout from the ABM Treaty and bring pressure for counterconcessions from us, perhaps involving the new Trident missile deployment.
The ABM Treaty was written in such a way that cheating, such as the Krasnoyarsk radar, would become apparent long before it became militarily significant. In this respect, the treaty has been a success. However, it is important not only to detect violations, but to redress them. The cure involves halting illegal behavior. It also includes controlling offensive buildups that lead either side to believe that its supreme national interests can be preserved only by abrogating the ABM Treaty. It appears unlikely that significant progress will be made in Geneva unless the US and the USSR express serious interest in both offensive and defensive arms control.
Michael Lewis is a physicist and strategic analyst residing near Washington, D.C.