Defense: why consensus crumbles

Until now there has been widespread and broadly based political support for the increased military spending initiated by the Reagan administration. Humiliated by the hostages in Iran, angered by the Soviets' invasion of Afghanistan, and disturbed by the erosion of US prestige around the world, the country welcomed an approach that promised to make America strong again.

Now the consensus for defense spending threatens to come apart. The prospect of huge budget deficits, drastic cuts in nondefense spending, and continuing inflation are causing questions not only about size of budget but also about the utility and cost-effectiveness of specific program investments. Grave risks may be posed to national security if the questions are not well handled.

The nature of our military weakness has been expressed quantitatively. The Soviets have more of everything: soldiers, tanks, aircraft, and missiles. This imbalance was vividly portrayed and widely disseminated in the glossy 99-page booklet, ''Soviet Military Power,'' prepared in 1981 by the Defense Department. That approach, concentrating as it does on static measures of superiority and equivalence, encourages a quantitative response to restoring the balance. So long as political support for vast increases in military spending continues, that response might provide us with adequate military strength eventually, although some spending might be unwisely targeted along the way.

A quantitative approach may be useful in expressing commitment, but only initially. Priorities can be refined over time, if there is time. But if a country comes to believe that military strength can be bought ''by the yard'' it will not have much difficulty in buying less when the economy or conflicting national priorities dictate.

Military effectiveness cannot be bought by increasing dollars across the board. The danger is that the decreases, when they come,

will be haphazard, even bureaucratic, political or geographical, and not related to the kind of defense posture that this country needs.

That may be unavoidable as a practical matter. But it is possible that more rational judgments would be made if there were greater understanding of the demands that may be placed upon our armed forces and the weapon systems they employ. This implies a public discussion of the kinds of war scenarios that military planners regard as most likely, and against which they develop force structure and procurement priorities.

It is time to question current assumptions. It is possible that a large-scale frontal attack by the Soviets in Central Europe, with a preceding lesser war in the Persian Gulf with the Russians, is not a likely scenario and distorts military planning. It may be overambitious and not realistic to prepare simultaneously to defend against an attack by North Korea against South Korea. Under what circumstances is it likely that the United States will go to war with ''surrogates''? This issue needs debate, especially now when questions are being raised about intervention in Central America.

There may be an alternative, more realistic set of scenarios against which we should be planning. Or, we may need to concentrate on the flexibility required to respond in different places in the world, in case we guess wrong.

We lack that flexibility now, and the Five-Year Defense Program only begins to give it sufficient emphasis. The scenarios have been made much more demanding by this administration, without adequate accompanying justification for the change in the threat assessment. And we probably overstate the reliability of the Warsaw Pact, especially now in light of the events in Poland.

Then there is the complicating factor of the competition for funds between nuclear and conventional weapons. In my view, early nuclear escalation will be made less likely by a strong conventional capability. But how much and what kind of nuclear programs best serve to deter must be argued persuasively. The antinuclear movement has a compelling simplicity that cannot be ignored.

These issues form the backdrop for all discussions of the effectiveness of the defense we are buying with our military dollars. The need for a 600-ship Navy, for large or small carriers, for more tactical aircraft and of what kind; for more tanks or more technologically advanced anti-tank weapons; more airlift; a new package of costly strategic nuclear weapons - these only make sense in a context of what military planners reasonably think may be required to deter or to employ.

The public must know what the weapons systems will be able to do, and how much they will really cost. There is growing suspicion about understated inflation, changes that will cause cost overruns, and general concealment of full program costs.

Critics are increasingly qualitative and sophisticated in their approaches. Spokesmen for the military reform movement make some persuasive arguments that we need greater numbers of simpler, cheaper systems that will not break down. They do not credit the US with a technological advantage in certain areas that might shift critical balances where the Soviets enjoy numerical superiority. And they equate technical advancements with complexity at higher failure rates. This is an appealing simplification, but may be more often wrong than right.

It is not that the defense budget is devoid of rationale. There are well-developed grounds for greater or lesser urgency for every choice made with the budget submitted to Congress. Some are powerful, others are spurious. Some choices are bureaucratic or frankly political. These especially need exposure to daylight.

Perhaps few people will take the time to sift through complex materials when offered. But the public is increasingly interested in what the critics have to say. The result of a failure to supply a serious, thoughtful, and detailed rationale by the Department of Defense for its budget priorities is likely to have serious consequences. Reductions may be made that leave our country with a lopsided military posture less capable of meeting real requirements than our armed forces were in 1977 before the first increases of the Carter administration.