Almost two years after candidate Ronald Reagan embraced a Republican Party platform calling for "the earliest possible deployment of the MX missile in a prudent survivable configuration," the future of the whole program is in doubt both politically and technically.

Partly because of the unanswered questions that still surround the missile, the normally sympathetic Senate Armed Services subcommittee on strategic and theater nuclear forces voted 9 to 0 Tuesday night to shut off money for deploying the MX on a temporary basis in existing Minuteman silos.

Subcommittee members reasoned that it would make no sense at all to expose the new MX to the same risks facing the older Minuteman missile, which is stationary underground and thus easy for the Soviets to target. The better idea, they agreed, would be to hold off on producing the missile until Reagan could do what he complained in the campaign his predecessor had not done: come up with a safe permanent home for the weapon.

This reasoning seems to be the majority view in both the Senate and House these days. Defense Secretary Caspar W. Weinberger's rationale for putting the first MXs in Minuteman holes, starting in 1986, was that it would be better than letting the missiles pile up in warehouses. The subcommittee suggested instead that the Pentagon simply slow down production so the missile would be ready at the same time its new home was built. This is likely to be 1989, or a three-year delay in the deployment the Republican Party said was so urgent back in 1980.

But there is a respected body of opinion that argues more fundamentally that the day of the land-based strategic missile is over; that U.S. and Soviet warheads have become so accurate that it is a losing game to try to make them invulnerable against surprise attack. Better to give up the triad of land, air and sea nuclear forces and settle for two of those three, a "diad," goes this argument, which helps explain why it has taken so long to find a suitable home for the MX.

Reagan's own advisory panel on the MX, headed by Charles Townes, professor of physics at the University of California, weighed in on this side of the argument when the president was pondering what to do with the new nuclear blockbuster.

"The committee investigated a broad range of ICBM intercontinental ballistic missile options," the Townes committee told Reagan last year, according to portions of its report just released by the Pentagon. "It finds no practical basing mode for missiles deployed on the land's surface, available at this time, that assures an adequate number of surviving ICBM warheads."

That statement leaves the air and the sea for the MX. Since the United States already is putting big nuclear missiles to sea aboard Trident submarines, the air looked to the Townes committee like the best place for the for the MX.

Wrote the Townes committee:

"The most promising approach to providing a new secure ICBM retaliatory force appears to be continuous airborne patrol. The committee believes that a new aircraft making use of today's composite material technology and fuel-efficient engines can be satisfactorily designed for such a mission. The committee thus recommends that the concept of keeping ICBMs on patrol over oceans and the continental U.S. be pursued to the extent of initiating a program for such an aircraft and proceeding promptly to concept formulation."

Weinberger last year was attracted to that idea of basing MX missiles in the sky aboard giant, "Big Bird" airplanes, even though the Air Force put down the idea as impractical. The Air Force wants to make the MX a mobile missile, one that could be moved from one shelter to another covertly, in hopes of convincing the Soviets that they could not not knock out the U.S. land missile force in a surprise attack. Reagan has rejected the Air Force's original mobile MX basing scheme, but an aerial MX is still an option--just as it has been for years.

With Congress well on the way to forbidding temporary basing of the MX in existing silos, and the experts at odds over what else to do with the missile, the debate is on its way back to square one. White House spokesman Larry Speakes said yesterday that the Pentagon "is disappointed" about the Senate subcommittee's action on the basing schedule, a remark that may turn out to be an understatement the way things are suddenly going against the missile.