The recent halting of MX missile flight tests {front page, Aug. 24} is a manifestation of a phenomenon that has become all too common -- the overestimation of the capabilities of weapons systems. Judging from the frequency with which it occurs, this problem is endemic to our processes of military procurement and development.

Although this is no doubt a simplification, it seems that the problem derives at least in part from a combination of two factors: a) the inclination of defense contractors to promise systems whose capabilities tax our most advanced technologies -- resulting from an understandable if not laudable "get the contract at all costs" mentality; and b) the Defense Department's reluctance to reveal flaws and inadequacies in its policies and weapons systems. The latter has been amply demonstrated in armed conflicts (Vietnam and Grenada) and weapons development (the Bradley fighting vehicle).

The frequent repetition of this problem in the development of what are comparatively simple weapons raises grave doubts about the reliability of the far more complex systems required by the Strategic Defense Initiative. Moreover, it stands as convincing testimony to the recklessness of entrusting our security to such systems and the imprudence of investing our resources in them.