IT USED to be that political scientists found it was pretty simple to sketch a diagram of the spectrum of political systems and beliefs. You drew a straight line: to the extreme left was communism, to the extreme right facism. The happy medium, not surprisingly, was Western-style democracy.

Over time, however, a few people noticed that communists and fascists had more than a few things in common. So the line went out, and the circle came in. Traveling too far in either direction led to the same unpalatable spot-totalitarianism. At the opposite pole, not surprisingly, was Western-style democracy.

But the Reagan folks in general-Defense czar Casper W. Weinberger '38 in particular-have a new vision of political systems that is sending government watchers scurrying back to the chalkboard. This time, however, not even trapezoids will do the trick.

At issue is the right to analyze and even criticize government policy, a fundamental tenet of democracy. The Reaganites are against it.

When the House Appropriations Committee recently issued a report warning that the readiness and stability of the U.S. Armed Forces had declined despite ever greater military appropriations, Weinberger countered by calling the report itself "dangerous." Although he did not challenge the facts of the study, Weinberger contested the report's conclusions. And he was quoted as saying, "the potential danger is that people, our foes and some of our friends, will get a wrong and incorrect impression of both our capabilities and our resolve." This, he added, "in this kind of world, where [impressions are] an essential part of deterrance, is. I think, a dangerous disservice to the United States."

What a tragedy if open inquiry is to become the next casualty of the Reagan-fueled nuclear arms race. Weinberger's evident dislike of military accountability, so offensive in Grenada, is nothing short of absurd when applied to evaluations like the House subcommittee's. What appears to concern Weinberger most is not the report itself, but rather the public airing of soiled Pentagon linen. This, despite the claim of Appropriations Committee Chair Rep. Joseph P. Addabbo (D-N.Y.) that the report had been "sanitized" by Defense officials prior to its release.

NEEDLESS TO SAY, it is Congress business to assess the state of U.S. military preparedness, particularly when faced with blockbuster Defense appropriation requests. And it is everyone's business to keep a watchful and critical eye on government performance, no matter what our "foes" may think. This is what characterizes our society as "open" from those the Reagan Administration has pledged to undermine as distastefully "closed," or totalitarian. Weinberger is certainly not the first to recognize the drawbacks of such openness on military security, but he is among the first to push for its subversion. Under this administration, the dictates of national security now require the dilution of the very political principles it was meant to defend.

Which is why Addabbo far more closely articulated the spirit of democracy as it is commonly understood, when he responded to Weinberger with the following remark, quoted in the Washington Post. "I think we do a great service to our national security," he said. "By publicizing the report and spotlighting it, maybe we'll get some attention to the waste and fraud."

At least some Pentagon officials apparently felt the same way when they issued a subsequent report suggesting that Army and Air Force preparedness had indeed decreased during the Reagan term. But Chairman of the Joint Chiefs of Staff Gen. John W. Vessey, who joined the Weinberger attack on the Congressional document, publicly disputed those internal reports, and the official military line is to second Weinberger's outrage.

Undoubtedly, what has administration officials so up in arms is not the philosophical, but the practical import of the studies. Despite record defense expenditures, military officials ranging from the Joint Chiefs of Staff to officers in the field have recently testified that the U.S. Armed Forces are I sufficiently equipped to conduct sustained conventional warfare. These criticims are a large political embarassment to the "get tough" Reagan team, already facing Congressional opposition to proposed defense funding increases. The relative preparedenss famine in times of Pentagon plenty must be attributed in large part to inordinate expenditures on nuclear over conventional forces and to wide-spread waste.

Assuming the critical reports do not have the calamitous effect of generating sentiment for still greater defense funds--to bolster conventional, along with nuclear forces--concern over military readiness could help stem the growth of the nuclear aresenal. The danger is that greater "preparedness" could mushroom into a dangerous build-up in conventional forces, but in general, any break on the nuclear effort would be a welcome change.

Perhaps more immediately significant, however, is the potential impact of the studies on military waste, for it is here that the Administration blind spot is most disconcerting. Granted Pentagon waste did not start in with the Reaganites, but clearly a fresh perspective is needed when President Reagan calls current U.S. aid to El Salvador--an amount which, according to published estimates allots more than $20,000 per Salvadoran guerilla--"niggardly," and likens the funding to "letting El Salvador slowly bleed to death." Clearly it is needed when, in the age of $50 screwdrivers and massive cost overruns. Weinberger says of inefficiency and corruption in Defense contracting: "there isn't any to start with, and it has no effect [on preparedness]."

But perhaps Weinberger should be excused for what one hopes is oversight, his economic textbook says massive inefficiencies and corruption only occur in closed systems--never in Western-style democracy.