MX rebuff may trigger shift in nuclear defense strategy

This week's congressional blow to the MX missile in its dense-pack plan - like an ICBM with many warheads - is likely to have widespread and explosive effects.

It signals significant rethinking about the triad of sea-, land-, and air-based nuclear forces. It calls into question the need for ever larger missiles and whether in fact they increase deterrence or add to the likelihood of nuclear war. It may alter arms-control negotiations between the two superpowers. And it could affect the plan to deploy the Pershing II intermediate-range missile in Europe.

Coincidentally, two significant events occurred the same day the House of Representatives voted against building the first five MX (Peacekeeper) missiles.

The Danish Parliament voted to suspend payment of its share of the Pershing II in Europe, a move that is sure to bolster the European antinuclear movement. West German Defense Minister Manfred Worner said here recently that failure to deploy the MX in the United States would cause many Europeans to ask why they should deploy the American-made Pershing II on their soil.

Second, the Air Force announced this week that the first squadron of B-52 bombers armed with nuclear-tipped cruise missiles now will be on daily alert status. Like the decision in Denmark, this also illustrates the fluid nature of nuclear weapons and strategic thinking at this time. More than economic considerations, this underlies congressional action on the MX.

There is a growing sense that land-based missiles (unless they are truly mobile) will always be vulnerable, given the accuracy of opposing forces. Growing ''counterforce'' capability (the ability to take out an enemy's strategic forces) has overtaken ''countervalue'' might (going after cities, industrial areas, and other ''soft'' targets). Thus, mutual assured destruction can no longer be counted on to deter a first strike. Strategic planning and arms-control efforts therefore are now being driven by technology.

This is reflected in the disclosure that most members of the Joint Chiefs of Staff don't think the dense-pack basing plan will work. The MX is also criticized by many retired senior military officers, including Adm. Noel Gayler, former director of the National Security Agency; Rear Adms. Eugene Carroll and Gene LaRocque of the Center for Defense Information; and Adm. Stansfield Turner, former CIA director, who says the MX is at ''the most destabilizing end of the weapons spectrum.''

It also is reflected in the comment by Rep. Charles Bennett (D) of Florida that ''the triad is not the Trinity.''

Deploying nuclear cruise missiles on upgraded B-52s gives the US a distinct advantage within the air leg of the triad. Critics of the MX also argue that a shift in emphasis toward submarine-based missiles and smaller, more mobile land-based ICBMs could reduce the likelihood of a first-strike attack by deemphasizing missiles that are large and threatening, but vulnerable.

Sen. Dale Bumpers (D) of Arkansas says it would be better to increase the number of smaller, single-warhead missiles rather than concentrate ICBM forces in large, static missiles. Sens. Gary Hart (D) of Colorado and Albert Gore (D) of Tennessee say the nuclear threshold would be raised if both superpowers agreed to replace multiwarhead missiles with a limited number of single-warhead ICBMs.

This would reduce the overall number of nuclear warheads, lessen the superpowers' counterforce (or ''countersilo'') capability, and thus lower the likelihood of either side launching a first strike, it is argued. Such a radical change in nuclear strategy would be accompanied by large costs and serious verifiability problems, it is acknowledged, but no less than the MX.

A move away from heavy, land-based missiles is supported by a recent Congressional Budget Office study. Using Air Force figures, the CBO concluded that ''even if closely spaced basing (dense pack) works and the MX survives in substantial numbers, the percentage contribution to United States strategic capabilities would be small.'' CBO analysts put this at 5 to 13 percent.

As the MX declines in favor, the new Trident II (D-5) submarine weapon also is being pushed as a ''common'' missile that could be deployed at sea or on land. It is only slightly behind the MX in development, but will be just as accurate. At 60 tons, it is bigger than the current Minuteman but smaller than the MX and thus could be easier to move about and less vulnerable.

Interservice rivalry has prevented development of a common missile in the past. But this could change with the current mood in Congress regarding the MX.