IN CALLING the NATO summit's attention to a Soviet military buildup "which far exceeds [the Soviet Union's] legitimate security needs," President Carter was in the fortunate position of having ready a program to meet the threat he described. The program, for long-term defense planning, has been in preparation for a year; NATO is accepting it now. It provides for small annual increases in real defense spending, improvements in force readiness and combat effectiveness, and economizing by cooperation on weapons procurement. When it comes to delivery on those earnest pledges, no doubt more than one NATO member will come up short. Thirty years of reliance on the American shield have glazed the determination of most European allies, West Germany conspicuously excepted, to meet difficult military challenges. The Carter administration's NATO initiative nonetheless has elicited about as firm a response as one could expect from a region as economically and politically troubled as Western Europe. There has been transatlantic consultation up, down and sideways. NATO is, in its fashion, doing what it was meant to do in preparing the defense of the West.

To be sure, not every member of NATO feels that is still the alliance's principal job. For one, Canada, secure under the American strategic umbrella, now is seized of the mission of setting an example of unilateral disarmament; it has withdrawn its Europe-based forces from any nuclear role, and is replacing with conventionally armed aircraft the nuclear-capable planes still assigned to its forces in North America. There is no country with which it would be more pleasant to take a stroll - on a sunny day. Turkey, for a second example, is so put out by the Cyprus-triggered American arms embargo that it is pretending - a pretension that events could move toward reality - that it finds NATO irrelevant. Prime Minister Bulent Ecevit spoke yesterday, vaguely but feelingly, of the need for NATO to go beyond deterrence into dialogue and mutual understanding with the Russians. One could instantly see why he is so highly regarded as a poet.

Notwithstanding such passing triumphs of fad and pique over national interest, NATO will endure. No other instrument is available to maintain the military balance essential to the physical protection and the inner equilibrium even of those members who are unable to give the alliance the attention that their dependence upon it requires. It is sometimes said that perception of the common Soviet threat is the glue of NATO. That really isn't so. At the core of the alliance is a common good nature, the feeling among the members of NATO that there is a preciousness to the defense and welfare of all of the democracies, regardless of the peccadillos of any of them. That the members - or, at any given moment, most of the members - are democracies builds in an empathy for the failings of the breed.