Is the Pentagon buying the right defense mix?

Beyond the astronomical Pentagon budget and its likely impact on the deficit, the debate over President Reagan's military buildup is turning increasingly to the kind of bang this administration wants to buy for its buck.

Is it too high-tech . . . relying on too many ''bells and whistles'' in Pentagon parlance? It's not just the relatively liberal military reformers and budget cutters who now think so, but more hawkish analysts as well. They look at all the fancy and expensive new gadgets and raise troubling questions: Will they perform as advertised? Will these weapons be relevant in any likely combat scenario? Recent wars and weapons testing suggest not, some experts say.

Many are concerned that the boost in weapons buying will come at the expense of more mundane but essential items like training and readiness. Some experts warn that the administration's recently proffered military pay freeze could make it harder for the military to attract and retain the skilled soldiers, sailors, and airmen necessary to operate and fix the new gear.

A report released Friday by the relatively conservative Heritage Foundation makes these points in considerable depth and detail. Some of its sharper comments:

''The increased spending secured by President Reagan should afford significant improvements in force size. It does not. . . . The readiness account is falling further behind actual readiness needs as more complex systems come on line . . . complexity greatly increases costs to buy and maintain equipment, and drives down the size of fighting forces while it increases the size of the logistics structure . . . overemphasis on long-shots technology has diverted attention away from the most vital considerations of all: leadership, tactics, and unit structure and training.''

This is one of the major points made by members of the bipartisan military reform caucus in Congress. It is backed up by recent findings of the Congressional Budget Office (CBO) and some Pentagon analysts.

Using administration data, the CBO estimates that the portion of the military budget spent on new weapons will rise steadily from 27 percent in 1981 to 39 percent in 1987. At the same time, the CBO predicts that funds for operations will drop from 33 percent to 25 percent of the Pentagon budget. This trend becomes more worrisome when the increased cost of operating the new weapons is considered. For example, the CBO warns that keeping the new M-1 tank in the field will cost 36 percent more than the existing M-60 tank.

An internal Pentagon study (disputed publicly by high-ranking officials) tracks the cost overruns of major weapons systems in recent years and concludes that the price for the current rearmament will inevitably be higher than predicted.

The Heritage Foundation report also details the reasons for such overruns, emphasizing that these are a lot more controllable than defense officials claim. But it also goes into broader issues of strategy and force planning that are important for the NATO alliance as well as American armed forces.

Current Air Force and Army planning and procurement are directed toward a new doctrine called Air-Land Battle. It relies on centralized control, unfailing communications, precise intelligence (much of it provided by remote sensors), and deep attacks beyond the immediate battle line, using sophisticated standoff munitions to defeat an aggressor.

The NATO commander, Gen. Bernard Rogers, sees the new doctrine as a way of deterring attack without resorting to nuclear weapons, and West German Defense Minister Manfred Worner is the chief European promoter of advanced Western technology to achieve it.

But there are those who fear that such a plan could fall apart during the uncertainty and heat of battle.

''A major performance shortfall for key sensors or long-range munitions, or confusion and delay in interpreting sensor data, would destroy the air-land scenario,'' says defense analyst George Kuhn, author of the Heritage Foundation report. ''Until combat can be tailored to technology, logic dictates that we not fool ourselves into thinking that technology will change the rules of the game.''

In a recent article in International Security Review, a Georgetown University scholar and defense consultant, Stephen Canby, writes: ''Technology may indeed offset poor military practice and organization. But it is cheaper, simpler, and more logical to remove the malpractices in the first instance.''

He suggests a structural realignment of allied forces, including more efficient use of European reserves and reorganized US forces to provide greater combat strength relative to support units.

Such critics by no means advocate a return to biplanes and bolt-action rifles. But they say the military's goal of a ''high-lo (technology) mix'' in weapons is weighted too heavily on the high side.

Mr. Kuhn and Mr. Canby aren't the first to note that the spectacular successes of the Israeli Air Force against its Syrian counterpart in the skies over Lebanon rested heavily on older technology. Most of the Syrian MIGs and surface-to-air antiaircraft sites were destroyed with Vietnam-vintage missiles.

Many of the Pentagon's high-tech, standoff munitions have done poorly in testing. Others rely on active radar, which can be detected by an opposing force. Prices of such weapons have risen dramatically as well. The F/A-18 Hornet jet - the ''lo'' half of the Navy's high-lo tactical aircraft mix - now costs $ 22.5 million. Yet it has not met its established standard in the attack role.

''The US equipment inventory is brimming with items that fail to meet their promised performance standards or the needs of combat,'' Kuhn cautions.

Because of the rising per-unit costs of such weapons as the M-1 tank, the Pentagon is actually buying fewer than earlier planned, although overall spending has gone up under the Reagan administration.

Thus the complex ''quantity vs. quality'' debate is sure to continue as Congress grapples with the new Pentagon budget.