In the Reagan administration's first month of office back in 1981, Defense Secretary Caspar Weinberger was asked whether in light of the defense increases then already heading into their second year, there might be some areas where big money could actually be saved. "Not really," said the man who had won the nickname of Cap the Knife for his previous budgetary prowess. He has been true to his word.

A few months later he was asked just what the administration intended to do with the big additional increases coming along. Little was to be gained, he warned, "by an early enunciation of some elaborate 'conceptual structure,' a full-fledged Reagan strategy. Too often, in the past, these easy and early pronouncements have caused real harm. They prejudged and oversimplified reality; they put blinders on our vision." Weinberger has been true to this word too.

Four years and a trillion dollars later, it is easier to see the gains and losses of the greatest military buildup in any nation's peacetime history.

The gains are there in the additional forces bought and in the measurable contribution they have made to American peace of mind -- measurable by, for instance, Ronald Reagan's reelection and by the greater security many people say they feel. Harder to measure but traceable nonetheless is the contribution that the last six years' military budgets have made to the confidence felt by American allies.

The losses are in the economic and social consequences of the Reagan budgets and in the squandering of the rare opportunity this strength-minded administration originally had to reform the "military-industrial complex," rationalize defense planning and build a more durable popular consensus on defense.

Running for office the first time, Ronald Reagan stressed the comfortingly conservative notion that a strong economy was the essential foundation of a strong defense. But as president he has often seemed to ignore that order of priorities and to proceed on the assumption that a strong defense could be built -- or because of dangers in the world had to be built -- on whatever economy we had. He has never stopped insisting that defense was the one category of spending that could not be subjected to economic constraints.

This is precisely the judgment now challenged on the Hill. The Senate has voted to freeze new money for the Pentagon at the current level plus inflation; the large amounts of old money in the pipeline ensure that actual spending will rise for years. The House is considering a freeze that would not compensate for inflation -- it would not reach the old money in the pipeline either.

Anxiety over the deficits, rage over procurement practices and a demand for equity in budget cuts finally created a critical mass and produced a broad assault on the president's leadership, the military's indiscipline and the civilian Pentagon's managerial style. As a result, Congress is starting to check the Reagan pattern, one that actually began in the last Carter year, of substantial and open-ended annual defense hikes.

Weinberger's response this week was characteristic and saddening: "Those who would have us do without modern equipment and make do with cheaper, less sophisticated models that we know would be inferior to the Soviets' have failed to add two things to their calculations: the quality of the Soviet equipment and the value of human life." This after a trillion-dollar surge that leaves military spending in steady dollars at twice the level where the administration began, and which is still going on, although at a reduced pace.

It is fair, however, to wonder what the Soviets will make of the new congressiona disposition to apply more financial discipline to military spending. In and about the administration, there is a certain apprehension that the Russians may be emboldened to hang tougher in negotiations and conflict situations. My own guess is that the Russians are no less likely to be sobered by the benefits to the United States, and the additional pressures on themselves, flowing from an American decision to hold the Pentagon budget at a still very high but more sustainable level.

The total of defense spending, almost everyone agrees, is an arbitrary and unreliable index of national strength and will. Undeniably, however, it is a convenient and accessible one. The symbolism of a rising figure had its fair political uses in recent years. The symbolism of a steady figure has its uses now.