THE folks at the Pentagon should not be overly exuberant these days, now that President Reagan has sided with Defense Secretary Caspar Weinberger in carefully limiting the amount of projected budget savings for the United States military.
The Pentagon may have won the internal White House budget skirmish. But in doing so it may well have set the administration up for a defeat in the biggest battle of all: gaining congressional support for the administration's program of deep budget cuts in nondefense spending.
Not all of the elements of the proposed Pentagon budget cuts are fully detailed as of this writing. But what is clear is that the cuts - as outlined - are not enough. On the social side of the budget, child nutrition would be sharply cut. The Small Business Administration would be abolished. Mass-transit operating funds would grind to a halt. And so on. But defense would basically sail right along as it is. Such a plan undercuts the administration's contention that its budget would fairly ''freeze'' total spending for fiscal year 1986 to reduce soaring federal deficits.
Congress should reject the administration's projected defense cutbacks and work toward the type of deeper cuts suggested by White House Budget Director David Stockman. The defense cuts now being broached by the Pentagon and White House would add up to around $28 billion over the next three years. By contrast, the Stockman plan would have cut some $58 billion from projected defense outlays over the next three years.
What is particularly disturbing about the proposed cuts - the $28 billion figure - is that they may not even add up, according to some nongovernment budget analysts. Congress will surely take a hard look at the actual numbers. Moreover, lawmakers need to ask specific questions: How can the Pentagon be better managed? Does the US really need to commit billions of dollars to the MX missile? How far should the US go with the administration's ''star wars'' space program, a program which Mikhail Gorbachev this week suggested the Russians would feel a need to match?
The issue is not one of slashing Pentagon budgets and thus weakening US defense. The administration plans spending close to $1 trillion for defense over the next three years. Rather, the issue is how to produce the best possible defense at the most prudent price.
The ironies abound. The Pentagon is a massive federal agency with extensive intelligence-spy-investigative units. Yet, despite all that, the Pentagon apparently has not picked up the fact that public tolerance is fast dissipating for sky-high spending, cost overruns, and fouled-up procurement practices at a time when budgets for popular social programs would be slashed to the bone. Why has the Pentagon missed this opportunity to show Americans that it too can tighten its belt and share in the larger budget sacrifice that is necessary? Were it to do so, the upshot would likely be increased, not lessened, public support for the American military.