Ironically, the changes in foreign and defense policy that impressed the Nobel Prize Committee were thrust on Mr. Gorbachev by the same domestic imperatives that now consume him and that may ultimately lead to his downfall.

Seventy years of Communist bungling had left the Soviet state a paradigm of inefficiency. Industrial quality existed only in pockets, and much of that was devoted to weapons production. The armed forces claimed up to twenty-five percent of a tottering GNP. In his reform program, Mr. Gorbachev cut military expenditures and diverted resources to domestic priorities.

He earned his Nobel Prize. Regardless of his motives, the world benefited greatly from his military retrenchment. At the same time, we must recognize that his primary objective is stopping the Soviet Union's slide toward oblivion. His aspirations beyond that are unclear. Whatever course he or his successors pursue, they will have massive military power at their disposal.

For Soviet armed forces, "less" is a relative term. They began reducing from a level of 214 divisions and 5,000,000 military personnel. They are now down to 190 divisions. Troop strength might fall as low as 3,000,000. That is reduction on an epic scale, but when (and if) it is done, Soviet armed forces will remain the largest in the world.

The same applies to war materiel. Soviet tank production is down by half, from 3,400 a year to 1,700. Thus diminished, the output still is approximately double NATO's annual tank production.

By US reckoning, the Soviets cut their military spending by about five percent in 1989, but Secretary of Defense Dick Cheney maintains that the new total is "higher than when Mr. Gorbachev came to power" and "at a level that will permit considerable Soviet force modernization."

Modernization is particularly intense in the strategic forces, which have also been protected from reductions. The ICBM force is in the midst of a complete upgrade. Quality improvements are evident in all of the Soviet combat arms. Tactical forces, for example, are responding to the reductions by junking older equipment and outfitting their slimmed-down units with better weapons.

They are already testing improved variants of their MiG-29 "Fulcrum" and Su-27 "Flanker." Two entirely new aircraft, the Counter-Air Fighter (CAF) to succeed the MiG-29 and the Air Superiority Fighter (ASF) to follow the Su-27, might show up by the end of this decade.

In 1987, the Soviet Union announced a new defensive doctrine. Like most Soviet dogmas, it tended toward ambiguity, but it made a break, at least nominally, with the concept of the large-scale offensive, which had dominated Soviet military thinking for forty years.

While the change is encouraging in a general sort of way, the Soviets themselves are not sure of what it means exactly. Soviet Military Power 1990, published in September by the Pentagon, points out that the "concept of a defensive doctrine seems to apply only to conventional forces, not to strategic forces" and that the Soviets are proceeding to build a force that, even with the limitations of a strategic arms treaty, will hold a first-strike capability against US missile silos and forces not on alert.

Furthermore, the defensive doctrine embraces a "strategic counter-offensive," the capabilities and training for which are similar to those required for offensive attack.

At the moment, the Soviet Union looks tame. Our attention is drawn to the reductions rather than to the forces that remain. Furthermore, Mr. Gorbachev has been a model of cordiality and conciliation in his conduct of foreign affairs.

We cannot assume these conditions to be permanent. The Soviet Union is not sure of its own borders, much less of its eventual objectives and relationships with other nations. It may not happen this year or next, but the time will probably come when the Soviets feel that their interests are threatened.

At that point, military power will be an awesome instrument of Soviet foreign policy. Mr. Gorbachev may still be in charge, but that is not an automatic assurance of peaceful behavior. He does not shrink from assertiveness when he believes the situation calls for it.

The inescapable factor in any speculation is the effective continuation of Soviet military power. As Gen. Colin Powell, Chairman of the Joint Chiefs of Staff, said in a speech October 15, "now and in the future, the Soviet Union will remain a military superpower," one that "I never forget has the capability to destroy the United States in thirty minutes."