THE QUESTION of American bases in Spain is in the news. Eager to join the West after the Franco decades, Spain entered NATO in the 1980s. With conditions: it refused to join NATO's integrated command or to admit nuclear weapons on its territory, and it insisted on a ''balancing'' reduction of the existing Franco-made American military presence. Now it seeks to remove three squadrons of American F-16s whose mission is, in crisis time, to take nuclear weapons aboard elsewhere and confront the Soviet Union. The United States has been hoping to keep some of the planes on Spanish soil.

Madrid is not the first member to want NATO's full protections and benefits at reduced cost. Nor is it the first to hold that it alone should determine the burdens and that the political convenience of the incumbent government must be served. As it happens, after Generalissimo Franco died in 1975, Spain's friends were quite willing to indulge the special requirements of decompression. So Spain was from the start something of an alliance freeloader.

As leader of the alliance, the United States cannot avoid concern over what are the terms of others' participation in the common defense and over how those terms are arranged. Leadership always comes down to balancing an assertion of American interests against a respect for others' interests -- interests and sensibilities. Over the years, Americans have done an extraordinarily good job of it, if you can stand back from the routine static and survey the general vigor.

But it is not ordained that this will continue, and meanwhile the alliance is entering a demanding phase. With the INF Treaty, the nuclear equation is starting to be rewritten. With the Soviet Union embarked on a peace offensive and the United States soliciting greater European burden-sharing, NATO's political equation could change too. This makes it foolish for Spain to act in the '70s way, on the premise that national convenience dominates, rather than make the extra '80s effort to work out adjustments within the alliance as a whole.

Spain is democratic now. Europe is healthy, with a population and product larger than either ''great'' power's. Yet Americans carry their old inflated share of defense. Europeans should not be laying down burdens, least of all unilaterally. Imagine their reaction if it were the United States that had gone unilateral and were pulling out its F-16s. Ostensibly Madrid's negotiation is with Washington, but it is the other Europeans who have the greatest incentive to bring the central lesson of collective security home to Spain.