PROPHETIC SCENARIOS fleshed out into popular bestsellers share one common flaw--they invariably prove wrong. To his credit, General Sir John Hackett, a former NATO army group commander with a string of letters dangling from his double-titled name, recognizes this.

Hackett knows as well as any of us that any effort to describe an international showdown between the U.S. and U.S.S.R. leading to world war can call to its aid only hypothesis and speculation, not prediction and calculation. Nevertheless, one can ask of our "top-ranking NATO generals and advisers" at least a little understanding of the international power structure they seek to preserve.

Even in the handful of months since its conception, Hackett's book has become laughably dated. The military details of tank strengths and armor-piercing capabilities Hackett keeps under rigid command and control, but the basic premises that lead him to conclude a European land war is conceivable fall out of his influence even as he tries to marshal them.

Consider his analysis of the Middle East. "The Shah's Iran" is "the only stable right-wing country in the area." Israel, with its powerful army, has become a neutral nation. And Egypt has once again swung over into the Soviet camp. Perhaps it would be spiteful to point out to General Sir John that, despite his access to top-secret documents, he has missed the basic point of recent U.S. military policy in the Eastern Mediterranean--to keep Israel as a friendly naval and air base in light of the instability of both Greece and Turkey.

Nitpicking aside, flaws like these cast doubt on the most basic premise of his book. The Third World War is a call to rearmament, a shrill blast of the trumpet for Western governments to boost their military expenditures now, before it's too late and the crawling armies of Bolshevism engulf what Hackett calls "the free nations of the Western world." He believes the advent of "flexible response" military policies in the sixties--abandoning automatic massive nuclear retaliation in favor of both conventional and nuclear forces--makes land war in Europe a distinct possibility over the next decade.

HE MAY WELL BE RIGHT. But his eagerness to prove a point blinds him to several important factors on which NATO political leaders (if not their military counterparts, Hackett inadvertently suggests) base their thinking. First, he assumes that generals on both sides will exercise self-restraint in the use of tactical nuclear weapons. No fighting force in history has ever believed it should not make full use of all available weapons, and battlefield nuclear equipment is abundantly available to both sides. Hackett avoids considering what effect the use of tactical nukes would have on the land war, on international public opinion, and on escalation to full-scale strategic nuclear war.

Hackett really loses his credibility, though, when he shyly evades the issues which should be at the core of any "third world war" scenario. Nuclear deterrence is a distasteful and outmoded phrase to General Sir John. In his rush to prove that "flexible response" makes a 1980s European land war a possibility, he conveniently forgets that this policy evolved to meet Soviet threats, real or perceived, in odd corners of the world. Places like Vietnam, not West Germany. European strategic thought should still be based firmly on the existence of nuclear stockpiles on both sides. If Hackett represents a style of thought fashionable among NATO military leaders, it's time they received some re-education in the realities of the post-World War II era.

YOU MIGHT FORGIVE Hackett his misunderstanding of modern strategic thought if he had turned out a well-written, entertaining tour of the next Armageddon. His account instead reads like a repair manual for a Chieftain tank upgraded for use on all NATO forces, with a simple refrain liberally repeated throughout--"What was done in the years between 1978 and 1984" (that is, Hackett nudges us in the ribs, what we should be doing right now) "was enough to prevent Soviet victory."

Some glimmer of literary understanding must have penetrated the fog of war in Hackett's brain, enough anyway for him to understand the need to place some human beings among the Phantoms and stereotyped initative-lacking Soviet junior officers in his narrative. Every so often he clumsily inserts a phony "personal recollection," most embarrassingly in a letter home from an American sailor:

Some of the soldiers who jumped straight overboard when the missiles hit were saved. But hundreds were lost. It was bad. We were lucky. A British frigate found us, and that's why I'm in Gosport, England, Mom. There's a great joke going around here that Britain's been saved by the US Calvary riding in--like those old movies, you know?

Towards the end The Third World War degenerates into pure fantasy, the pipe-dream of Cold Warrior too old to stay on the front line but too fevered to give up the good fight. China and Japan have formed a "co-prosperity sphere" in Hackett's rosy future, and play no part in the war. Valiant Afrikaaners defend their homeland from the incompetent assaults of Soviet-supplied Namibians and Zimbabwians. As the Soviet drive into West Germany falters, Soviet satellites rebel, soldiers stop fighting, and a high-level coup in the Kremlin leads to a break-up of the entire Soviet Union--the internal contradictions of Marxism-Leninism, y'know?

Hackett should have tried writing a straight-forward account of the strengths and weaknesses of opposing forces in Europe, something he is probably competent to handle. Instead, he has coated his diatribe for rearmament with a nauseating layer of future history, complete with fake footnoting and eyewitness accounts. But then, the derision Hackett opens himself to makes it less likely anyone will listen to his argument--which is just as well.