When President Reagan unveiled a plan last October to stick the troublesome MX missile into existing, although strengthened, silos across the West, the Pentagon and Capitol Hill fairly spluttered with disbelief.
The Senate has now made it clear that it regards the proposal, a crucial element of the administration's drive to enhance the nation's strategic warmaking ability, with extreme disfavor. But the President warned Congress Thursday that he will not tolerate any tampering with the strategic enhancement plan he announced Oct. 2.
By a vote of 90 to 4 on Dec. 2, the Senate approved an amendment denying the Pentagon most of the money it sought to devise the most effective means of strengthening Titan and Minuteman silos to receive the MX. The action effectively diverts $334 million of the $354 million earmarked for such silo research instead into the examination of alternative basing schemes for the missile.
''The MX is simply not survivable in existing silos - whether hardened or unhardened,'' declared Sen. Sam Nunn (D) of Georgia, a member of the Senate Armed Services Committee, who sponsored the amendment with Sen. William S. Cohen (R) of Maine. This view is shared by Gen. Richard Ellis, former commander of the Strategic Air Command, now retired, who claims that even ''the experts'' do not know how to harden existing missile silos to a point where they could survive the megatonnage the Soviets would throw at them.
Senator Cohen insists the Pentagon should lose no time in examining other basing systems for the MX, including a variation of the so-called multiple protective shelter (MPS) plan that President Carter endorsed and his successor scrapped. The MPS deployment involved shuttling 200 MX missiles around 4,600 underground shelters in the deserts of Nevada and Utah.
In announcing his plan for revitalizing the US strategic deterrent, President Reagan declared that while deploying 30 to 40 MX missiles in existing silos, three long-term basing plans for the MX would be examined. They involve launching 60 to 70 missiles from aircraft, deploying them deep underground, or providing them with ballistic missile defense (BMD).
But, according to the magazine Aviation Week & Space Technology, the administration has not abandoned attempts to base the MX as President Carter wanted. It claims that the Pentagon has already established an executive committee to explore such deceptive basing for both offensive ballistic missiles and for BMD systems.
If the magazine is accurate - and Defense Secretary Caspar W. Weinberger denied he was contemplating an MPS basing mode for the MX last October - the creation of such a committee should mollify Senator Nunn. He maintains that even an interim basing mode for the MX should be ''compatible with mobility, deception, and ballistic missile defenses.''
Senator Nunn, whose grasp of defense topics is renowned, contends that the placing of MX missiles in silos is ''the most ill-conceived and ill-advised'' part of the President's strategic enhancement plan.
In his view, the Soviet Union might interpret such a deployment to mean the US was prepared to launch its MX force on warning of a Soviet missile assault. The Soviets might then adopt a similar policy, he warned, thus placing ''a hair trigger'' on nuclear forces in both the US and USSR.
Secretary Weinberger has conceded that the Soviet Union will shortly have the ability, ''if they get an absolute direct hit, of causing some damage within one of those even strengthened silos.'' But he emphasizes that Soviet strategic missiles still lack accuracy. The defense secretary says that it is vital to deploy the MX in ''as survivable a mode as we can as quickly as it comes off the production line.''
Denying that silo-basing the MX constitutes the ''final, permanent ultimate solution'' to the vexed problem of deploying the missile, Weinberger insists that it provides ''a few valuable years at a time when we don't know of anything else.'' As he sees it ''the very fact of deploying the MX in a silo from which it can be launched has a substantially increased deterrent effect, and it is important to have it there rather than in a warehouse.''
The defense secretary has conceded that considerable strides need to be made in BMD technology for it to be effective. But doubts persist in the defense community that the MX could ever be adequately protected by such a system. Deep-basing the MX and stowing it aboard continuously patrolling aircraft are both ''promising'' means of deploying the missile, according to Weinberger.
If no survivable system can be devised for the MX, say defense analysts, the age of the land-based strategic missile may be over. Weinberger does not anticipate its imminent demise.
As the Senate considered a $208.5 billion defense appropriations bill Dec. 3, Sen. Ted Stevens (R) of Alaska read the letter from President Reagan in which he warned that rejection of any part of his strategic weapons plan would lead to dangerous US inferiority vis-a-vis the Soviet Union.
The President said that the rejection of any part of his strategic enhancement package would undermine the US negotiating position ''at the very outset'' of the current Geneva talks to reduce the number of medium-range nuclear missiles in Europe.