In the arcane, theoretical world of nuclear strategic doctrine, the most important word is rather simple: stability. Any decision to research, build, or deploy a nuclear weapon is shadowed by the key question of whether such action is likely to increase or decrease the chances of nuclear holocaust.
This theme runs through the recent report of the President's Commission on Strategic Forces, the high-level group charged with finding a home for the MX missile. And it is likely to be the key to whether Congress approves this most controversial part of the Reagan administration's strategic modernization program.
Between the descriptions in military-speak of silo superhardening, warhead fractionation, and prompt hard target attack, the MX commissioners warn and worry about nuclear stabilization. Some form of the word ''stable'' is used seven times in a single page, and ''stability'' is defined in the glossary along with terminal guidance, post boost vehicle, and penetration aids.
The bipartisan group concludes that deploying the MX in old Minuteman missile silos (along with developing a smaller, single-warhead missile and moving arms control efforts toward counting warheads rather than missiles) in the long run will increase nuclear stability .
Many independent experts and members of Congress, however, fear just the opposite. They say that putting the 10-warhead, very accurate MX in fixed, known locations will move the United States closer to a ''launch-on-warning'' doctrine. This means that in times of extreme superpower tension or conventional fighting, the missiles could be fired - not in retaliation, but in response to warnings of a Soviet nuclear attack.
''That really is the danger,'' says a member of Congress wrestling with the MX funding decision.
Similar warnings were being made about the MX even before the recent commission report, and they have increased in number and volume since then.
Physicist and nuclear weapons designer Richard Garwin says that no matter what the basing mode, ''10 warheads on a single missile simply provide too tempting a target to the other side.'' University of California strategic studies director William Van Cleave (who headed the Reagan administration's defense transition team) agrees.
Its short flight time and high accuracy put MX at ''the most destabilizing end of the weapons spectrum,'' warns Stansfield Turner, a former Central Intelligence Agency director and retired admiral.
''If there ever was a 'use it or lose it' system, ill-designed for stability in crisis, it is this one,'' McGeorge Bundy wrote of the MX commission recommendation.
In a recent New York Times column, Mr. Bundy, a former presidential national security assistant, wrote: ''Because the MX has 10 warheads, not the two that is the average of the Minuteman force, it will be five times as vulnerable, warhead for warhead, as Minuteman itself. . . . A system of this kind is open to only one protective device, a capacity for launch-on-warning - for rapid firing on possibly fallible electronic notice of an incoming attack.''
Chief SALT I negotiator Gerard Smith has called the MX ''an inherently destabilizing system,'' and a former Joint Chiefs of Staff chairman, Gen. Maxwell Taylor, says land-based ICBMs should be replaced by safer sea- and air-launched weapons.
Many senior Air Force officers and MX-supporters in the past have rejected placing the missile in Minuteman silos. MX commission member William Perry (a former undersecretary of defense) said in 1981 that doing so ''simply increases the hair trigger . . . on both sides.''
The commission played down the question of US ICBM vulnerability. But presidential science adviser George Keyworth said recently, ''Right now the Soviet Union can effectively destroy our Minuteman fleet in a first-strike, using only 25 percent of their ICBM fleet.''
Would this prompt the US, under pressure, to launch its MX missiles in equally vulnerable Minuteman silos? Recent congressional testimony on the new MX/small missile plan revealed this concern.
Under senatorial questioning, the chairman of the Joint Chiefs of Staff, Gen. John Vessey, and the Air Force Chief of Staff, Gen. Charles Gabriel, did not rule out the possibility that the US might ''launch on warning'' rather than ''ride out an attack'' before retaliating. US strategic doctrine by design has always been somewhat vague on this point. But some lawmakers worry that it could be forced in this direction by leaving its most militarily valuable missile relatively vulnerable.
If anything, the Soviet Union is worse off. Some three-quarters of its strategic warheads are on fixed, land-based missiles (compared with about one-quarter for the US). The threat to its 600-plus SS-18s and 19s (its top-of-the-line ICBMs) would increase markedly with deployment of 1,000 very accurate MX warheads. Would this lower the nuclear threshold on the Soviet side?
The MX commission argues that the US must be able to ''put at risk'' those missile silos, as well as protected command and control facilities, just as the Soviet Union now can threaten US ''hard targets.''
''A one-sided strategic condition in which the Soviet Union could effectively destroy the whole range of strategic targets in the United States, but we could not effectively destroy a similar range of targets in the Soviet Union, would be extremely unstable over the long run,'' the report warns.
As with the doctrine of ''mutual assured destruction,'' more technically complex deterrence is largely a matter of perceptions. Whether the MX is perceived as helping or harming nuclear stability will determine its future.