A LOT OF THE critics of Ronald Reagan's MX program, like those who criticized Jimmy Carter before him, argue that as there is no problem, the MX is no solution -- only a gigantically costly and provocative enterprise. We think they are wrong. There is a problem. But the newly proposed Reagan response does not resolve it. Rather, the so- called Dense Pack MX response may only serve to perpetuate the problem, to take the whole exotic business of who could do what (theoretically) to whom in a nuclear war to a further realm of expensive, but inconclusive, competition.

The problem to which the administration is responding is this: the Soviet Union has developed an arsenal of intercontinental ballistic missiles greatly larger both in numbers and in power than our own, and these have the capacity to destroy most of our own land-based missiles in a preemptive strike. Several administrations have concluded that neither the smaller American ICBMs nor our sea-based missiles or strategic bombers have an equal capacity vis-Ma-vis the Soviets' land-based ICBMs. The United States could not destroy them in a preemptive strike because we do not at present have enough weapons of either sufficient accuracy or weight to do so. So in this sense the Russians have a clear advantage. Defense critics who have spent the past 15 years arguing that the Russians would not possibly be so spendthrift or so foolish as to develop precisely the kind of arsenal they have in fact developed are singularly poorly placed, we think, to argue now that the Russians probably would be too scared to use it or that it probably wouldn't work or whatever the latest nostrum is.

True, this Soviet capability is theoretical; and the chances of its being exploited are extremely remote. But the problem is no less real for that. We ourselves have no doubt that in a dread nuclear war, the whole preposterous antiseptic "scenario" business (they do this, then we do that, so they do this . . . and so forth) would be the first thing incinerated. There are more than enough nuclear weapons on both sides now to guarantee that there would be no winners, and the Russians, unless they are true idiots, must know this, too. But a situation in which a large and central part of one side's nuclear deterrent force is vulnerable, even in theory, to a wipeout attack by the other is a prescription for all that is worst in relations between nuclear-armed states: anxiety, suspicion, bullying, miscalculation, lack of confidence, over-quick responses, now-or-never thinking. It cannot be acceptable for this particular situation to persist.

The Reagan administration, like the Carter administration, now seeks to redress the imbalance in two ways. One is by deploying a blockbuster missile (the MX) that is big and accurate enough to do for the Soviet land-based missiles what their SS18s can do for ours: destroy them in their silos. The other is to make a portion of our land-based ICBM forces, specifically these new MX missiles, safe from such Soviet attack; we will try to bury them in such a manner and configuration that no SS18 can reach or destroy them all. That is what the Dense Pack burial plot is all about. It supersedes the Carter administration's peek-a-boo mobile MX scheme, a different kind of technique for trying to get some landbased ICBMs out of harm's way.

The best that can be said for all this is that conceivably it will have some impact on Soviet conduct as a pressure, as a "bargaining chip." That is clearly the hope some of the MX's adherents have for the new missile itself, a missile whose actual development and deployment after all would only create a world in which both sides, rather than one side, stood poised with weapons that it would pay to fire first. And, even then, even if this rather problematical basing scheme did work, what exactly would that mean? Work for how long and against what countermeasures and at what cost in inevitable further refinements and protections and schemes to dig ever deeper and build ever bigger and more?

There will be much argument now over what kind of walls can withstand what kind of shocks, argument over guidance and impact and explosion effects and the rest. And there will also be much argument, equally speculative, over what the effect of all this will be on Soviet policy. But in a sense these are tactical, short-term concerns that miss the major point. They assume there is some practical, economically feasible way of making our land-based ICBM force invulnerable to enemy attack. Everything we know about the subject suggests that this is not true. The history of the past couple of decades has in fact been a history of costly, escalating and eventually doomed efforts to bring about this much desired outcome. When something is pronounced vulnerable, from a carrier to an ICBM, it is somehow forbidden in certain quarters to accept that it is terminally vulnerable and to go on to better substitutes. Instead, the great attempt to add on features of "invulnerability" gets going.

That, it seems to us, is where this country is now in the great MX debate. Bright people (until they go into government, when they shut up) talk about alternatives to our huge land-based missile system, talk about putting more at sea, less on land, talk of developing some residual land-based mobile missiles but giving up this hugely costly and ultimately impractical insistence on protecting an essentially vulnerable stationary system. We do not presume to judge now the technological or tactical merits of the Reagan Dense Pack proposal, the yeses and nos of the smaller arguments to be resolved within the framework of its larger strategic assumption that the land-based missiles can be made secure. We begin somewhere else: we think the basic assumption is mortally wrong.