The administration's plans for addressing Soviet military power are at the center of international as well as American debate these days. Here William W. Kaufmann, a defense planning expert, looks at the Reagan defense budget with a beady eye, and Richard Burt of the State Department makes the case for one especially controversial weapon the administration intends to deploy in Europe--the Pershing II missile.

How much does the United States need to spend on defense during the next five years? The Reagan administration proposes $238.6 billion for fiscal 1984 and a total of $1,553.6 billion between fiscal 1984 and fiscal 1988.

Although the president indicates that this is a rock-bottom amount, a case can be made that U.S. security will be better served by canceling or stretching out some of the investment programs that will be responsible for half of these large expenditures, by holding active-duty military personnel at current levels, and by using some of the savings for acquisition of additional conventional forces that are readily available and deployable. For once, in fact, it seems possible to get more real defense for less money.

Consider U.S. strategic nuclear forces. These constitute the foundation on which the more useable power of the United States and its allies rests. It is eminently desirable to have high confidence in their retaliatory power; we can have that kind of confidence at the present time.

Right now, the strategic offense is capable, even after a well-executed Soviet surprise attack, of delivering at least 3,000 nuclear warheads on targets in the U.S.S.R., and that number will increase to more than 4,000 as additional Trident submarines and air-launched cruise missiles (ALCMs) are deployed during the next five years. Even so, prudence dictates that the strategic offense remain both diversified and capable of destroying a wide variety of targets (including hard targets) in the face of Soviet efforts to undermine it.

Prudence, however, does not require the deployment of two ballistic missiles with a hard- target kill capability, two heavy bombers in close succession, two versions of the ALCM, or a submarine-launched version of the nuclear cruise missile. Nor does prudence necessitate any rush toward the deployment of a technically questionable ballistic missile defense, a more modern continental air defense that could be destroyed by ballistic missiles, or a few pieces of a command-control system ostensibly designed for the conduct of a protracted nuclear war that no one understands how to fight or to terminate.

In short, nothing but a few campaign pledges would be lost by eliminating the most obvious redundancies and excesses in the administration's program for modernizing the strategic forces. More specifically, cancellation of the MX, the B1, the modernized air defenses and several of the more exotic sensors based in space, and deceleration of the program for ballistic missile defense, would save more than $57 billion in outlays over the next five years without in any way jeopardizing the retaliatory power of the strategic forces.

Conventional forces are what give the nation its real military leverage, and it is considerable, despite repeated and mystifying efforts to downgrade it. Current U.S. ground and tactical air forces, in conjunction with allied capabilities, have a high probability of conducting a successful forward defense if concentrated in a single theater such as central Europe, even against a major attack by the Warsaw Pact. Existing U.S. naval forces, together with allied fleets, are fully capable of holding open essential sea lines of communication to Europe, the Persian Gulf and Northeast Asia.

However, all the conventional capabilities are in need of gradual modernization. Furthermore, in light of continued Soviet efforts to improve their own conventional capabilities, it would be politic to hedge against the possibility of having to deal simultaneously with major crises in Europe, the Persian Gulf and Northeast Asia. National Guard and Reserve forces, if given more modern equipment and additional training, are now sufficiently large to provide the necessary insurance.

Considering the relatively measured pace with which the Warsaw Pact can be expected to mobilize and deploy fully combat-ready forces, fast sealift would be the most efficient way to deploy U.S. reinforcements to the threatened theaters. That, however, is not the direction in which the administration is going in its programs for the conventional forces. It has acceded to the Navy's long-held but unexplained ambition to deploy 15 carrier battle groups and four surface action groups built around battleships. It has also agreed to an accelerated modernization of the Army and Air Force and to a large increase in stocks of modern munitions independently of how long the Warsaw Pact and U.S. allies are capable of fighting.

The only specific justification for the expanded Navy has been the ill-digested notion of carrying a conventional war to Murmansk and Vladivostok in retaliation for a Soviet attack elsewhere. Modernization of the ground and tactical air forces not only is taxing their absorptive capacities; it is also ensuring an expensive redundancy of aircraft with the production of three different types for close air support and another four for fighter and attack missions.

By holding the Navy to 12 carrier battle groups and halting the recommissioning of at least two battleships, by slowing the Army's modernization to a manageable pace and canceling a questionable program for the production of binary chemical weapons, by procuring modern munitions at a lower rate, and by eliminating three of the seven different types of tactical aircraft--preferably the AV-8B, the F14 and the F15--on the order of $98 billion in outlays could be saved during the next five years. Of that total, nearly $20 billion could be allocated to the improvement of the combat power and effectiveness of the National Guard and Reserve, still leaving a net saving of $78 billion.

What is more, at least 32 fast sealift ships could be acquired for the price of the additional airlift, which is now planned but is unlikely to add significantly to the rapid deployment capabilities of the United States in the late 1980s. These new ships, together with eight others already acquired, existing airlift and equipment already prepositioned in Europe and on board ships in the Indian Ocean, would make U.S. deployment capabilities commensurate with the dimensions of the threat toward the end of this decade and with the scale of the U.S. reinforcements that can be available by then.

The administration's five-year defense program will provide more rapidly, more luxuriously and more redundantly the military capabilities already sought by the Carter administration in the late 1970s. But it will not appreciably change the numerical imbalances about which President Reagan has expressed such concern.

However else the so-called military balance may evolve by 1988, one thing is likely to remain constant: the Soviet Union will continue to outnumber the United States in ballistic missiles, military personnel, tanks, artillery pieces and a great many other items of military equipment. If these differences are the measure of the window of vulnerability, the window will remain just as open with the administration's defense program as without it.

In actuality, of course, there is no military crisis of the imminence and scale described by the administration. If there were, it would make sense to put the strategic forces on a higher state of alert, reinstitute conscription, declare a national emergency and call the National Guard and Reserve to federal service. These and other quite feasible steps would permit the delivery of more than 1,000 additional warheads on a second strike and nearly a doubling of U.S. conventional forces in the near future.

But such draconian measures are not what is needed. This is not 1939, and a pell-mell mobilization is not what is required. The United States already maintains a large and powerful military establishment.

What is needed for the future is a gradual and orderly modernization of existing forces, higher readiness and modest insurance against the possibility of multiple crises around the perimeter of the Soviet bloc. Capabilities of the size and effectiveness necessary to satisfy these needs can be acquired within a real increase in defense total obligational authority of somewhat less than 6 percent a year. The outlays of $1,553.6 billion projected by the administration would be reduced by $135.5 billion.

Even so, the nation's security would be increased by more than is being proposed under the administration's current plan.