THE SPANISH election returns show rising confidence among the voters, both in themselves and in the parliamentary process. The first two elections after Spain's return to democracy, five years ago, cautiously returned coalitions of the center. This time, the Socialists, under young and energetic leadership, have won a clear majority. A substantial counterweight has simultaneously emerged in the form of a right-wing party under a former minister of the Franco regime. Since democracy ought to provide real choices, these developments are healthy and hopeful for a form of politics that a lot of Spaniards still regard as an experiment.

Americans will be slightly apprehensive about the future of the NATO bases in Spain. There was some Socialist campaign rhetoric about Spains dropping out of NATO altogether. But the incoming premier, Felipe Gonzalez, has indicated that perhaps not very much will change there very soon. Similarly, the Socialists, profiting by unhappy French experience, have carefully avoided any large commitments to nationalization of businesses.

Instead, the central preoccupation of the next Spanish government is likely to be the economy -- the unemployment rate is 15 percent and the inflation rate is 12 percent a year. Spain is now moving toward membership in the Common Market, and not all of the immediate effects are going to be welcome. Many Spanish industries have prospered only because international ostracism of Franco's fascism, for 30 years after World War II, provided them a degree of protection from their European competitors. But the impact of Common Market membership will go well beyond economics. The fascist presence isolated much of Spanish life from the main currents of European culture. That's been changing since Franco's death eight years ago, and it will change faster as commerce with the rest of Europe broadens.

To the reactionary right, the whole course of events seems an attack on Spanish tradition in its most distinctive forms. The reactionary right correctly identifies the present political system as crucial to this evolution, and will doubtless continue to challenge it. The Socialists are well aware of the danger, and evidently intend to go to some lengths to avoid providing targets to their enemies. They have one enormous advantage, in that time is on their side. This election is an important stage in the process by which Spain, in a sense that goes far beyond trade and money, is rejoining Europe. It is not excessively optimistic to hope that these developments have now reached a point at which they are irreversible.