The foreign policy implications of military spending - the shape as well as the size of US armed forces - are driving the debate over Pentagon budgets these days.
According to some analysts, the United States is attempting to do too much and is assuming that military force (or at least its threat) is more useful than in fact it is. This, in turn, leads to wrong choices in what to buy for defense, it is argued, and can be destabilizing.
''Fortress America'' puts it too simply, although many in Congress want to reduce the US troop commitment, especially in Europe.
But the debate comes down to finding the proper balance between protecting genuine US security interests and influencing regional situations that may not threaten this country; and it involves the admittedly difficult business of analyzing and projecting the intentions of the Soviet Union as well as its military buildup.
Lebanon, Central America, and the strategic nuclear balance are only the most obvious examples as Congress gropes with the number of MX missiles to fund or whether to approve an increased number of Army divisions, Air Force air wings, and Navy battle groups.
''While military power cannot create solutions to certain kinds of problems or create the kind of society we want, military power can sure destroy it,'' said Tidal McCoy, assistant secretary of the Air Force in a recent Pentagon discussion. ''It can sure leave you with fewer options than you had before. You can end up with a lot less if you don't have the clear capability and willpower to employ force as a last resort to protect your vital interests.''
Defense Secretary Caspar W. Weinberger frequently asks defense critics which alliance or treaty obligations they would have the US renounce in the name of austerity. Some who disagree with his policies pose the same question.
''There is only one way to cut defense costs - that is, for more than one or two seasons, or without hopelessly unbalancing the very forces that are counted on to perform whatever residual missions they are assigned - and that is by cutting force structure,'' writes Earl C. Ravenal in a new study titled ''Defining Defense.''
''That, in turn, means eliminating the missions of these deleted forces,'' argues Dr. Ravenal, a former Pentagon official who now is a professor of international relations at Georgetown University. ''And that implies substantive changes in our foreign policies.''
Ravenal says that the United States should adopt a ''noninterventionist'' defense policy that would provide sufficient national security while saving billions of dollars. In essence, he proposes a freeze on US defense spending, followed by a period of ''disengagement'' over the next decade. This would not (for example) result in the ''Finlandization'' of Western Europe, he says, but would cause US allies there to become more self-reliant.
Elsewhere, he says, ''the list of feasible interventions is far shorter than the list of desirable ones, and is even shorter than the list of 'necessary' ones.'' This is the fundamental question Congress faces with the mining of Nicaraguan ports and vast US military exercises in the Caribbean and Central American region.
Another prominent defense analyst, Robert Komer, faults the Reagan administration for its overreliance on nuclear weapons and on the push for ''maritime superiority.'' Mr. Komer, a former senior Pentagon official and ambassador to Turkey, stresses in his new book, ''Maritime Strategy or Coalition Defense?,'' the need for a better-equipped and -organized alliance defense of Europe.
Komer takes a decidedly different tack than Ravenal in suggesting that the US could be judged guilty of ''global unilateralism'' for trying to defend its interests too much on its own.
The administration's maritime strategy (especially the emphasis on new large aircraft carriers) ''will compromise our ability to help hold onto Europe, Japan , and Persian Gulf oil,'' he charges, and would be ''a recipe for disaster if deterrence fails.''
''The United States is simply stretched too thin,'' he warns, citing a ''mismatch between strategy and resources. Indeed, the essence of contemporary strategy decisionmaking is to face up to the necessity for tough choices when we cannot do everything we want.''
''The Reagan administration, though seeking great increases in US defense spending, has ducked this necessity for choice,'' Komer concludes.
A third well-respected defense expert says that the Reagan administration has both overstated the military threat to the United States and undervalued the strength of this country, particularly in concert with its allies.
This is William Kaufmann of the Massachusetts Institute of Technology, a Pentagon consultant for many years, who - under both Republican and Democratic administrations - played a key role in writing Defense Department ''posture statements'' (the annual rationale for military spending).
In his recent analysis of the administration's five-year defense program, Dr. Kaufmann states that the US, ''barring an unexpected change in Soviet practices or dramatic technological advances . . . can adopt a long-term investment strategy that is substantially more prudent than the current and costly rush to modernize.''
In this case, ''investment'' refers to spending for military procurement, weapons research and development, and military construction, where Kaufmann finds ''numerous examples of duplication.''
By eliminating such duplicated weaponry as accurate ballistic missiles, large bombers, tactical fighters, and air defenses, Kaufmann estimates that the Pentagon could save $174 billion through 1989. A more realistic assessment of threats to this country - and elimination of such ''questionable objectives'' as being able to ''take the offensive against naval ports in the Soviet Union'' rather than concentrating on improved sealift and sealane control - could raise that savings to $267 billion over five years, he calculates. Where US defense resources go:
in billions * Defense of Europe $129 * Defense of Asia $47 * Rapidly deployable forces $59 (including the Persian Gulf) * Strategic nuclear forces $70 Source: 'Defining Defense: The 1985 Military Budget,' by Earl C, Ravenal