How 100 MX missiles would look to the Russians

The case against the MX received an unexpected boost from the findings of the Scowcroft commission. The commission report, since endorsed by President Reagan, officially acknowledges that America's national security does not depend on survivable land-based missiles, since the United States has wisely dispersed half of its strategic nuclear warheads on invulnerable (and totally mobile) submarines. As acknowledged by the Scowcroft commission, the MX is not necessary for deterrence.

Turning to the more important question of the strategic nuclear balance, how would deployment of 100 MX missiles affect international security?

Consider the impact on Soviet nuclear forces: The USSR now deploys about 75 percent of its nuclear warheads on 1,398 potentially vulnerable land-based ICBMs. Only 900 of US warheads, mounted on modernized Minuteman 3 missiles, have sufficient accuracy and yield to destroy ICBMs in their underground silos.

Thus today the Soviets can rely on at least 500 missiles surviving the worst conceivable US attack. These 500 missiles, with something like 1,800 nuclear warheads, are more than adequate for deterrence. Therefore they can afford to wait out any US nuclear attack (or accidental launch, or false alarm from early warning radars, etc.). There is crisis stability with today's nuclear arsenals.

Deployment of 100 MX missiles with 10 warheads each would change this situation dramatically. The US would then have 1,900 silo-busting warheads, enough to theoretically threaten most of the Soviet strategic arsenal. With only 200 or so SLBM warheads normally at sea, the Soviets would be much more likely to fire their ICBMs at the first sign of attack or false alarm.

Both sides would have strong incentive to strike first in some future international crisis if the MX is deployed: the Soviets to avoid losing their ICBMs and the US in an attempt to limit damage by destroying Soviet missiles before they leave their silos. Clearly, the MX is destabilizing.

Indeed one could conclude that the hard-target, counterforce capability of the MX will never be utilized unless the US strikes first; otherwise it will hit nothing but empty silos. As for limiting Soviet reloads with spare missiles, high accuracy is not necessary, particularly because all but 60 of the 1,398 Soviet ICBMs are liquid-fueled, and direct hits are not needed to disrupt the liquid-fueling operation.

If the MX is unnecessary and destabilizing, why did the Scowcroft commission recommend deployment? Basically, the reasoning diverges from logic to the realm of perceptions: We must show our ''resolve'' to force the Soviets to negotiate. Just as President Carter endorsed the MX in the hopes of obtaining SALT II ratification, we are being told we must deploy the MX to stimulate arms control agreements.

It seems doubtful that the Soviets would ever agree to limit nuclear arms once the US has developed the capability to destroy 75 percent of its warheads. Certainly they would develop and deploy a new generation of nuclear weapons to regain their retaliatory capability before negotiating. They could choose to build more SLBMs, in an attempt to achieve the same submarine force survivability enjoyed by the US. However, Soviet submarines are generally acknowledged to be far less reliable than their American counterparts, with only 15 percent at sea at any time, compared to 60 percent for the US. Furthermore, the US antisubmarine warfare (ASW) capability is far superior to that of the USSR, so that the Soviets cannot be sure that their submarines will remain invulnerable in the 1990s.

Therefore, the likely Soviet response to the MX deployment would be to build a new generation of ICBMs. To regain their current status of 500 survivable missiles against 1,900 accurate US warheads, they would have to deploy another 1 ,000 ICBMs. This would hardly be conducive to arms control.