Among weapons experts and war planners, there is increasing acknowledgment that heavy, land-based intercontinental ballistic missiles - like the MX - cannot be relied on for very long to deter nuclear war. This realization is driving much of the debate in Washington these days, and underlies the report of the presidential Commission on Strategic Forces released Monday.
''Reasonable survivability of fixed targets, such as ICBM silos, may not outlast this century,'' warns the commission report.
The recommendations of this blue-ribbon and bipartisan panel of experts already had entered - and been influenced by - the public discussion of nuclear strategy. The recommendations include: housing 100 MX missiles in existing Minuteman and Titan missile silos, developing a smaller single-warhead mobile missile, and pressing ahead with anti-missile defense research.
The idea, said commission chairman Brent Scowcroft, is to increase superpower stability by initiating major new departures in both strategic weaponry and arms control. This would mean shifting to a count of warheads rather than launchers (as is now the case) while inducing the Soviet Union to join the move to single-warhead missiles.
Putting the MX in existing silos already has been rejected once by Congress, which deleted MX production funding from the current defense budget. The administration wants to spend $6.6 billion on building the first missiles during fiscal year 1984. Thus, while the commission's recommendations reflect some growing congressional sentiment on smaller mobile missiles, the political battle is far from over.
Deployment of the MX missile is likely to hinge on two things: whether the Air Force can convince lawmakers that they can find a way to ''superharden'' silos so that a significant number of MXs and new smaller missiles could survive (and thus deter) a Soviet attack; and whether the Reagan administration can convince Congress (especially those leaning toward a nuclear freeze) that the MX is needed as an indication of ''national will and cohesion,'' as Mr. Scowcroft put it Monday, to achieve ultimate real arms reductions.
On this politically delicate point, the President is not expected to embrace the commission report until the full House votes on a nuclear weapons freeze resolution later this week and the Senate votes on Reagan's controversial nominee to head the Arms Control and Disarmament Agency.
The administration has softened the tone of its rhetoric concerning nuclear war, making special effort to separate itself from past comments about such wars possibly being ''sustained,'' ''protracted,'' or ''limited.'' Injecting the MX back into the limelight could revive such controversial notions just as the Reagan administration is fighting as never before to preserve its steadily growing defense buildup.
For example, the Congressional Budget Office recently reported that the ''prompt hard-target kill capability of ICBMs and especially of the MX could be particularly important in a limited nuclear war featuring a series of exchanges, when it would be critical to destroy Soviet targets promptly before they could launch another attack.''
This, in essence, is the argument for the 10-warhead MX. But, increasingly, the missile is being seen by strategic experts, as well as key politicians, as a weapon whose time may have come and gone before it was ever deployed.
Sen. Malcolm Wallop (R) of Wyoming has called it ''the brainchild of wrong-headed thinking about nuclear war.''
Physicist Richard Garwin, designer of the earliest US atomic bombs and an adviser to the MX commission, says flatly there is no way to survivably base a missile like the MX that weighs 191,000 pounds and can't be moved about.
William Kaufmann, a Massachusetts Institute of Technology professor who has advised defense secretaries over the past two decades, recently reported for the Brookings Institution that the United States could retain adequate retaliatory strategic strength without the MX (or the B-1 bomber).
Sen. Ernest F. Hollings (D) of South Carolina, a member of the Senate defense appropriations subcommittee, says the US should ''leapfrog'' the MX and accelerate deployment of the Trident II D-5 submarine missile (which will be as accurate as the MX, but less vulnerable) and the new single-warhead mobile missile dubbed ''Midgetman.''
The Pentagon is not overly enthusiastic about developing a new small mobile missile as suggested by the commission and such congressional experts as Rep. Albert Gore Jr. (D) of Tennessee. But Pentagon officials acknowledge that they will have to accept this notion if they are to expect any cooperation from the Congress in approving MX production.