MILITARY OBJECTIVES IN SOVIET FOREIGN POLICY <i> by Michael MccGwire (Brookings: $39.50, hardcover; $18.95, paperback; 530 pp.)</i>

Since the 1960s, when he was chairman of the Senate Foreign Relations Committee, former Sen. William A. Fulbright has been asking why the Soviet Union would invade Europe.

Michael MccGwire, a senior fellow at the Brookings Institution, has spent the last five years looking for an answer, bringing to bear his skills as a foreign policy analyst and his experience as a British naval attache in Moscow and a former head of British naval intelligence.

He concludes that when Fulbright started asking the question, Soviet strategic doctrine provided every reason to expect a Soviet invasion of Europe if war seemed imminent. But a watershed decision in Moscow in 1966 started washing those reasons away until they are down to an eroded few.

His search for an answer has led to an important book, one based, first, on a tedious but crucial rummage through Soviet military writings and, second, on a look around to see whether Soviet writing squares with Soviet deployment of army, navy and air forces.

The tedium of research does not spill over into the final product, which is as gripping as a mystery novel and free of technical jargon (except in four major appendixes). To provide balance, it should be required reading as a companion to splashier offerings such as the Defense secretary’s annual report, “Soviet Military Power” (Government Printing Office: $7.50) or the 1987 White House publication “National Security Strategy.”

As an analyst, MccGwire is most proud of his detective work in identifying 1966 as the year when Moscow began to shift away from its 1950s assumption that war would inevitably lead to an all-out exchange of nuclear missiles that would devastate the Soviet Union and the United States.

For the Soviets, this shift ended their vision of an apocalyptic showdown between communism and capitalism. (The Pentagon still says in the 1987 edition of “Soviet Military Power” that “Soviet writings state that a future war would be a decisive clash on a global scale between two diametrically opposed socioeconomic systems. . . .”)

By now, Soviet military doctrine regards avoiding the use of nuclear weapons as its most important objective. MccGwire thinks it was this objective that sparked the Soviet interest in a 1972 treaty limiting the use of ballistic-missile defenses and more recently in proposals for major reductions in missiles and warheads on both sides.

The Soviets have wanted to cut back on nuclear missiles for nearly two decades but didn’t say so for fear of weakening their negotiating position. That, coupled with what MccGwire calls the “oversophisticated theory of arms control,” has led to useless expansion of weapons on both sides.

For armchair strategists, 1966 may be less interesting than MccGwire’s conclusion that a Soviet blitzkrieg across Europe would be an offense offering the best defense, to occur only if Moscow decided that world war could not be avoided.

Soviet doctrine, he writes, assumes that if they invaded Europe and avoided the use of nuclear weapons, the United States would do as it has in the past--crank up its superior industrial capacity and prepare to counterattack, not through Europe, but from the East. That thinking, he says, accounts for the buildup of Soviet naval strength in the Pacific.

MccGwire sees Soviet strategy flowing from five objectives: protecting the Soviet state (not the people, but the state); protecting the Communist Party; preserving “the capacity for independent action,” a requirement you can find on any national capital’s list; avoiding world war, and, if war cannot be avoided, managing not to lose.

He finds no evidence to support the Washington view that an expansionist policy drives the Soviet military buildup. If expansion were the Soviets’ game, he writes, one prime target would be the Persian Gulf area, but the Soviet commander in charge of that theater has the lowest priority in men, arms and equipment.

MccGwire’s major complaint about strategic thinking in Washington is that it is the kind of thinking a colonel must do when he has a regiment committed to battle. It is appropriate in those circumstances to assume the worst and shift men around to cope with it, but it is not the kind of view that “should underlie foreign policy.”

It would be folly to rearrange U.S. strategy on the basis of one man’s research and analysis, even when the work is as meticulous and persuasive as MccGwire’s. The only folly to match it would be ignoring what he says.

MccGwire’s conclusions should force a great debate on future U.S. defense policy and on the strategic Defense Initiative, or “Star Wars,” in particular.