The real explanation of Western Europe's rising fears of limits on NATO's use of ground-launched cruise missiles is more military than political: the need for the cruise to balance the immense Soviet force buildup in what are called Central European "theater" weapons.

The political factor, which leaves U.S. NATO allies feeling victimized by superpower-strategic-arms agreements, is bad enough for West Germany, England, France and lesser NATO allies. But truly critical to the future independence of Western Europe, these middle-level powers feel, is the necessity for NATO to compensate for the Soviet buildup. Otherwise an explosive crisis within NATO seems inevitable.

Even though the much-discussed medium-range crisis missile has not yet even been tested or officially asked for by NATO, the West Europeans perceive it as the answer to Soviet proliferation of a formidable array of new weapons systems.

To grasp the momentum of this buildup, consider these facts brought together in a recently desclassified NATO study:

In the four years ending last December, the Soviet Union has produced (largely for Central Europe) 13,85O front-line battle tanks, including the newest T-72 model, against U.S. production of 2,345; 6,500 long-range artillery pieces, the latest of which (a 155-mm) is believed capable of firing a nuclear explosive, as againt 800 in the U.S.; 5,500 fighter aircraft (including the third-generation MIG-27 now appearing at a 1,000-a-year rate) against 2,800 U.S. fighters.

European members of NATO - particularly the British and West Germans - have been eyeing the ground-launched cruise missile as perhaps the only possible counter to this buildup. Indeed, both London and Bonn (and the French only slightly less so) perceive in the presumably hard-to-shoot-down cruise missile a partial answer to vastly increased Soviet "theater" fire-power, with its thick antiaircraft defenses, and to the new SS-20 intermediate-range mobile ballistic missile.

"London wants a ground-launched cruise of 2,000 kilometers [about 1,200 miles], the French and Germans about 1,500 kilometers," one NATO expert told us. "That would bring western Russia, where the SS-20 is believed most deployable, within range."

But pressed by Moscow, the United States is perceived here to have tentatively agreed to a 600-kilometer range limit. With high government officials in London, Paris and Bonn receiving their first thorough briefing on these classified matters only last week (by Leslie Gelb, No. 1 State Department adviser on SALT), there is no doubt at NATO headquarters that only a hardline European appeal might now deflect President Carter from the agreement he seems wedded to: no transfer of U.S. cruise missile technology to the Europeans and no "circumvention" permitting deployment of medium-range cruise missiles in Western Europe.

The Carter administration belittles these European fears. Gelb, according to experts here, is saying that the ban on the range of over 600 kilometers will last only three years ("just a moratorium"). The NATO experts counter privately that if the European appeal is tough enough, Carter will be compelled to ease the nontransfer and noncircumvention language.

Few here predict that the huge Soviet buildup of Central European military power threatens sudden attack. The fear is different: that politics depends on perceptions and that, with Warsaw Pact military power clearly moving so far ahead of NATO's the Soviets are now perceived as approaching the kind of superiority that could insensibly lead Western Europe to buckle to Soviet economic and political pressures.

That is the answer to the recurring question of "why?": Why is Moscow spending 14 per cent of its gross national product on arms (more than twice the U.S. rate) and why has its conventional firepower in Central Europe almost doubled in the past four years?

As the Europeans see it, the answer is eventual brutalization of Europe by stockpiled military power skillfully manipulated for political and economic ends. For example, French planners say Finland's absorption - in the political and economics sense - by the Soviets has advanced much further than generally understood. They add that Moscow wants and economically healthy Western Europe - not one devasted by war - to provide the Soviet Union with an endless stream of technology and expertise.

This is the heart of the argument now heating up between Europe and Jimmy Carter. It is a military argument that today centers on the cruise missile, tommorrow on something else that the United States will be pressured by Moscow to withold from its allies in the interest of superpower diplomacy. Foreseeing this, top NATO officials here are betting on "an explosion within NATO" on the cruise-missile issue by early next year - one that will severely test U.S. desires for strategic arms pacts with Moscow at the expense of U.S. loyalty to the Europeans.