THE MX MISSILE, despite its repudiation last Monday in the House of Representatives: remains high on the Pentagon's wish list, and President Reagan has vowed to "take his case to the country" to save it Reagan's concern stems from a frightening but increasingly popular story. The story runs as follows: By 1984, the Soviet Union will have built enough ICBMs to destroy, in one blow, all of America's land based missile force. The Soviets will seize this golden opportunity having labored for decades to achieve it) and launch the attack, targeting our land-based missiles but leaving cities intact. With the entire American ICBM force annihilated, the President will have to choose either to surrender, or to retaliate with the remainder of our defenses submarine-launched missiles and bombers--and thus provoke a Soviet strike on American cities

The "window of vulnerability" to such attack, Reagan believes, extends from to 1987 But we need not despair, the Administration assures us, because, for only 35 billion, we can build the MX missile system, which will be safe from the new Red Peril Like its predecessor the "missile gap," however, the window of vulnerability is illusory. The Soviets, like us, could not rationally count on "winning" a nuclear war in one strike, so they are no more likely than we are to launch one

The first strike scenario assumes that the Soviets will accurately he able to destroy any missile by launching many missiles at it. But so far no has demonstrated that missiles targeted on a side will actually hit it. What has been demonstrated (and led to the military's claims of accuracy") is that many missiles shot in the same direction will land on the same spot--not necessarily the one at which they were aimed Wind and the electromagnetic effects of nuclear explosions will cause an unknown but significant amount of deflection. There is no military point in having five nuclear missiles land all together half a mile from their target. They would annihilate the neighborhood but leave a properly "hardened" silo intact.

Missiles might not destroy a silo even if they hit it dead-on. Destroying the silo requires the combined explosive force of all of the missiles. But if one of them explodes first, the resulting blast will destroy or at least deflect all the others. This "fratricide" theory remains unproven, but it forms the core of the justification for the "dense pack" basing mode proposed for the MX. If it will work for the MX, as the Administration claims, then it should work for the existing Minuteman silos, which can be hardened relatively cheaply.

EVEN IF IT WORKED, targeting our silos would hardly be worthwhile for the Soviets. An attack on our land-based missiles with theirs would cancel out both sides' first-strike capability. Meanwhile, our submarines and bomber forces, larger and more likely to survive than their Soviet counterparts, could adequately attack Soviet cities and military targets other than silos. After a first strike, the United States would emerge with more and better nuclear weapons than the Soviets.

But simply counting the number of pieces left on the board is not all there is to the game; nuclear war is a lot messier than that. Though experts debate the precise environmental impact of numerous nuclear explosions (a first strike would require thousands), they are certain of at least two potentially catastrophic effects. The ozone layer, which protects the Earth from lethal ultraviolet radiation, will disintegrate, and vast quantities of deadly radioactive fallout will scatter throughout the atmosphere. The original argument against nuclear war still applies to Soviet strategists. No attacker, no matter how formidable his arsenal, can feel secure triggering these dangers. Only the insane could launch such an attack, and only the credulous should fear it. --David V. Thottungal