WE DON'T KNOW whether the latest claimed convergence between military practicality and traditional science-fiction fantasy -- the so-called particle-beam weapon -- has any reality to it. But given the difficulties of Soviet-American arms-control dealings on such above-board matters as numbers and explosive yields of standard strategic weapons, it might be useful for some recognized authorities knowledgeable in these matters to try to forestall the mischiefmaking opportunities inherent in misty rumors of serious secret weapons of any sort.

As has been periodically reported over the past year or so, particle-beam weapons, PBWs for short, are supposed to spew forth enormous charges of subatomic particles, which, moving at the speed of light, can, presumably, shatter an incoming missile far from its intended target. Unlike laser weapons, whose light-based beams can be thwarted by clouds or atmospheric clutter, PBWs, in principle, are weatherproff and instantaneous in their kill-power.

An ideal weapon, some would say -- including the leading bellringer of the alleged PBW gap, retired Mau. Gen. George J. Keegan, the former head of Air Jorce intelligence. He's concerned that the Soviets have advanced so rapidly in PBW research that they are within two or three years of fielding a PBW weapons system. In his view -- amplified by Air Force rooters and assorted arms-control skeptics -- this looming, unliateral Soviet PBW capability, if unmatched, would be tantamount to dismantling the U.S. strategic missile force.

To the limited extent that the Defense Pdepartment has publicly addressed the subjuct, it has merely said that, while PBWs bear watching and exploratory research, military applications are at present remote and may never be practicable. But, as the administration also pointed out, in its annual arms-control impact statement last July, an effective PBW system might have tumultuous effects on existing agreements and future negotiations having to do with arms control

Meanwhile, there are knowledgeable scientists who argue that it is doubtjul that the particle-beam principle can be embodied in a utilitarian weapon, since the energy imput for an effective beam would have to be enormous. And, assuming that this problem can be overcome, they say, it would not be difficult to fool a beam defense with phony warheads and electronic decoys.

Lay onlookers to this controversy in esoteric science and technology may well feel inclined to the puzzlement and frustration that can be created when highly specialized doctors disagree. We don't think, however, that this latest entry in the weapons race eigher needs or deserves a screen of anxiety-producing secrecy around which partisans of various motives can exchange selected arguments.

For purposes of public assessment, what is fortunate about particle-beam technology is that, acientifically, it is a direct derivative of particle physics -- what used to be called "atom smashing" -- which is one of the most public and open, though highly complex, fields of modern research. Thus, if PBWs are theoretically feasible, there is little chance that this insight could be confined to either side, especially sine partical physics -- in which the United States is the world leader in machines, people and research results -- is a heavily traveled area in Soviet-American reserch collaboration.

What is important at this obviously early stage in the particle-beam chapter of the arms rece is that before discussion of the subject gets out of hand, the basic scientigic and technical realities ought to be publicly sorted out. For this purpose, an independent assessment by a broadly based group of independent physicists -- perhaps convened by the American Physical Society, the National Academy of Sciences or the American Association for the Advancement of Science -- would be a boon to public understanding and an antidote to selective leads.

It it turns out -- which is, of course, possible -- that PBWs are indeed militarily feasible, then it is none too early to start laying the groundwork for an informed public discussion of their arms-control implications.