To Congress's reluctant MX backers

Many congressmen appear willing to support the latest plan to deploy the MX missile in Minuteman silos because they believe it is the best means to force the Reagan administration into serious and substantive nuclear negotiations.

They admit that the new missile would be every bit as vulnerable to Soviet attack as existing Minuteman missiles. But these reluctant supporters argue that the MX should be approved because it is a necessary interim step to building the new Midgetman missile, and because approval of the MX would send a signal to the Soviet Union of a bipartisan consensus in support of both strategic modernization and arms control.

Unfortunately, these assumptions and others are based on leaps of faith that threaten to turn reason on its head.

* Assumption: The MX is a necessary interim step before we develop the Midgetman missile. Most people agree that the US should consider developing a small, single-warhead missile such as the proposed Midgetman, because our land-based nuclear arsenal would be less tempting to the enemy if our warheads were dispersed on a large number of single-warhead missiles. MX proponents argue that during the decade it will take to develop Midgetman the MX should be deployed as an interim step to replace the aging Minuteman missiles.

The problem is that once the MX is built, the Midgetman, which is clearly a lower priority program than the MX for the Air Force, may never be built. Future administrations and future Pentagon leaders may or may not decide to build Midgetman in the late 1980s. MX, rather than leading to Midgetman, may crowd it out.

* Assumption: By building the MX, we will force the Soviet Union to agree to deep reductions in its strategic arsenal. While it is conceivable the Soviets would respond positively to a US approach that combined deployment of MX with a call for cuts in strategic arms, it is at least equally likely that they would respond by producing a new, large MIRVed missile. Indeed, such a new Soviet missile is already well along in its development and testing. Administration officials have made it abundantly clear that we will not bargain away our 100 MX missiles as part of any agreement, so it is difficult to see how a non-negotiable item on our side will produce tangible concessions on the Soviet side.

* Assumption: A corollary argument is that the MX would put the Soviet force at greater risk and therefore force the Soviets toward a more survivable mobile missile. This would be a positive development for us, because the more vulnerable the missiles are on either side the greater the chances are for an accidental nuclear exchange. But there is little in Soviet history to suggest that the Russians will scrap the large investment they have made in their existing heavy missile force in response to any new US deployments. It is just as plausible that, recognizing the MX as a first-strike weapon, they would go to an even more hair-trigger, launch-on-warning concept to protect their land-based missile force while building new MIRVed missiles.

* Assumption: Congress can keep the administration on a short leash by authorizing a small number of MX missiles. The argument here is that Congress can force the administration to engage in serious arms control by authorizing only a portion of the total 100 missiles requested.

But history indicates two problems with this. First, Congress is a collection of 535 different wills and is therefore in no position to keep any administration on a short leash. Recall that former Secretary of Defense Harold Brown promised in 1978 that, if Congress approved the sale of ''stripped down'' F-15s to Saudi Arabia, the administration would never come back asking for enhancements of AWACS aircraft. Yet this is exactly what a new administration did only three years later.

In the second place, once production of a new weapon system is begun, it is extremely difficult to turn it off. A coalition of political, military, business , and labor interests will resist any effort to stop production. Congress can make a show of limiting initial MX procurement to 35 or 50 or 75, but it is likely that 100 or more will actually be produced and deployed. After all, proponents will argue, the start-up cost of the MX would be relatively high; the cost of additional MX missiles would be relatively low.

* Assumption: Building the MX and Midgetman would not violate previous arms control agreements. Developing two new US missiles would clearly violate existing SALT constraints. The future of Midgetman itself is clouded by whether a deployment mode can be found that is both survivable and verifiable. And there is likely to be a future effort to develop and deploy ballistic missile defense systems to protect the MX field, a move that would almost certainly require amendment or abrogation of the 1972 ABM treaty.

* Assumption: MX is the price we must pay for rebuilding a bipartisan consensus for arms control. The MX is an issue that divides Congress and the American people as perhaps no other weapon system has. The fact is that there was a fairly strong bipartisan consensus for arms control that extended through Republican and Democratic administrations from Eisenhower to Kennedy to Johnson to Nixon to Ford to Carter. It was the extreme right represented by candidate Ronald Reagan in the 1970s and by President Ronald Reagan in the early 1980s that broke the consensus by seeking to abandon existing arms agreements and goals.

There is no evidence to suggest that, even if Congress accepted all the Scowcroft commission recommendations, the administration would suddenly develop enthusiasm for nuclear arms agreements. An administration determined to achieve arms control does not need to be pushed into it, and an administration hostile to arms control cannot be forced into it. It should also be pointed out that, while the Scowcroft commission report embodied a bipartisan consensus, it was a consensus only among those who were committed in advance to finding a way to save the MX.

* Assumption: It is impossible to separate the MX from the other elements of the Scowcroft commission package. Notwithstanding the attempt to mold a new ''holy trinity'' - MX, Midgetman, and arms control - Congress will vote up or down on a simple resolution approving the proposed plan to deploy the MX in Minuteman silos. Public Law 97-377 establishes clear-cut procedures that will produce a vote only on whether Congress approves the release of FY 1983 funds for full-scale engineering development of the latest MX basing mode. Congress will not at that time be in a position to vote on the other elements of the Scowcroft commission recommendations.

We are all tired of hearing the MX debated. Some have developed the attitude, ''We've been discussing this thing so long let's just get on with it.'' But it is the wrong system. It is expensive, to be sure. More important, it ultimately could prove to be not the ''bargaining chip'' that its supporters suggest but a move that would open a new and more terrifying chapter in the nuclear arms race. We can find a better system around which to build a bipartisan consensus.

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