Leaving aside what the loss of Western Europe to communism would mean to the Europeans, what would it mean to us? Unless the Reagan administration and its most vocal supporters are prepared to say it wouldn't mean all that much, they ought to elevate the guns a little lower in their campaign to conscript our NATO allies for a global war against terrorism.

There is, first of all, the question of credibility. Those who regularly wring their hands over communist encroachments in, say, Yemen or Angola cannot expect to be taken seriously when they suggest that if the Europeans won't follow us to the shores of Tripoli, we will warn our tourists away from Europe, pack up our military forces, pick up our nuclear marbles and go home.

To talk that kind of nonsense is to suggest that our commitment to Europe's defense is not as much in our security interests as it is in Europe's. It is to ignore the care that was taken to define NATO's tight focus on maintenance of military forces to defend the territorial bounds of Western Europe against Soviet attack. We risk not having NATO at all when we seek alliance solidarity in behalf of far-flung ventures that some of the partners believe are misguided on their merits or contrary to their national security.

That is the curse of "unilateral globalism" -- the new vogue so dear to conservatives in and out of the administration. It presupposes a snappy salute from NATO allies for an attack on Libya to avenge the death of an American soldier at the hands of a Qaddafi hit squad. The administration's case rests on the right granted in the U.N. Charter to "self-defense" -- which is not necessarily the same thing as alliance defense.

But if that is the U.S. argument, why should the Europeans be denied their right to decide that what may suit America's "self-defense" may not necessarily suit theirs? A little history is helpful.

In the fall of 1956, President Eisenhower was tending to domestic political considerations: his reelection to a second term in November. The Soviets were brutalizing Hungary. Peace was the issue. American oil companies, meanwhile, were working their way into the Persian Gulf and striking it rich.

Whereupon, one week before Election Day and behind the back of the United States, our three best friends, the British, the French and the Israelis, launched an attack on Egypt. They had assorted, urgent national security interests. Israel wanted to stamp out what it took to be state-supported terrorism, directed by Egypt's President Gamal Abdel Nasser. France would have been pleased to overthrow Nasser, who was supporting the rebels against the French in Algeria. Britain wanted to regain the Suez Canal, which had been seized earlier that year by Nasser.

Did the United States salute? In no way. Eisenhower demanded and got a cease-fire with the Franco-British-Israeli mission unaccomplished. The following year, the Eisenhower administration forced the Israelis to give back the Sinai to Egypt. But the Europeans, however deeply embittered, did not accuse the Americans of cowardice or greed -- or of knuckling under to domestic political pressures.

The alliance recovered, with a lesson learned. In the best of all possible worlds, you might suppose that a partnership of reasonably like-minded, free nations ought to be able to engage together in defense of one or all of its members from whatever hostile source, whatever its location.

In the real world, however, West Germany, Greece, Canada, Norway, Portugal and France -- to name just a few members of NATO's mixed bag -- have too many different outlooks to agree even among themselves, let alone with the United States, on common action for common purposes beyond the one they signed up for.

That's not to say that some or all of them cannot work together, case by case, on problems that go beyond NATO's original mission. But when the United States tries to browbeat its European partners into automatic obedience, it risks overloading the alliance to the breaking point. NATO's narrow focus is the price we pay for an alliance that has shouldered its proper burden with a degree of success unparalleled in history.