The new Basque autonomous region recently approved in a referendum by the Spanish Basques is a country with a long memory, and it includes a grievance against the United States.

It is a grievance the Basque nationlist establishment has been nurturing against the Americans since World War II, and it illustrates how a great power's policy decisions in relatively remote places can come back to haunt it years later.

The story of what the nationalists regard as the unpaid American historical debt to the Basques is considered by them as fundamental to any understanding of recent Basque history, and it could profoundly affect the evolution of the new entity. If it ever became independent, it would at least be distrustful of a United States that many Basques consider to be guilty of betrayal.

The Basques say they were encouraged to believe that after the United States and its wartime allies defeated Nazi Germany and fascist Italy, it would overthrow Generalissimo Francisco Franco, the fascist dictator Hitler and Mussolini had helped to power. So, the Basques say, they threw themselves wholeheartedly into the U.S. war effort, believing that it would result in the restoration of the Basque homeland that Franco suppressed in the Spanish civil war.

Instead, Franco stayed in power another 30 years with the Americans as his major foreign supporters.

"Now is the time," said Carlos Garaicoechea, the nationalist leader considered most likely to become the first president of the reconstituted Basque country, for the United States to start paying its debt to the Basques.

Failure to restore a democratic government in the Basque country also resulted in the prolongation for more than 30 years of an atmosphere of international intrigue and spying. Wartime San Sebastian, the Basque intellectual capital, was a notorious center of intelligence rivalries in a Spain whose formal neutrality in World War II attracted the rival spy organizations of Europe.

The conspiratorial atmosphere seems as thick as ever.

"Even before we set up our own Basque police, we're going to need to reconstitute an intelligence organization," said Roman Agesta, an old Basque intelligence man, now Paris branch president of the mainstream Catholic-oriented Basque National Party. "The old operatives are all there, just waiting to be pressed back into service."

As a professional foreign observer of the Basque scene said: "After 40 years or more of clandestinity, it's very hard for them to work in a normal environment."

On orders from the head of the Basque government-in-exile, Jose Antonio de Aguirre, during World War II, the Basques mobilized their strong communities and their intelligence organization throughout Latin America to counteract German and Spanish propaganda and spy efforts.

Basque agents on Spanish ships got the German naval code for the allies. Basque agents penetrated Nazi intelligence. Basque mountaineers smuggled downed airmen from the allied forces out of France, across the Pyrenees and Spain. A unit recruited among Basque refugees was armed and trained by the Americans and took part in the liberation of Bordeaux.

"We worked for the allies, and we didn't get anything in return," said Pedro de Beitia, the unofficial Basque national representative in Washington from 1952 to 1977. He conceded that nothing was actually put in writing, but he said it seemed inconceivable to the Basque leaders that the Americans would not help them overturn Franco.

Moderate Basque nationalists trace the origins of ETA, the Basque terrorist organization, directly to the signing of the military base agreements between Franco and the Eisenhower administration in 1953. Young Basque nationalists then started expressing deep frustration over their elders' continued faith in American aid.

The Basque National Party's relationship with the Americans was terminated in about 1958, when Franco felt sure enough of his U.S. connection to demand that the Americans end their support for the moderate Basque resistance group. It was then that ETA really gained momentum as a breakaway alternative.

Basque unrest has served as a magnet for Israelis, Arabs and the great powers, too, not to speak of the intelligence organizations of Spain and France, who have a direct stake in the Basque region's political evolution.

There have been recurring reports of Soviet and other East Bloc involvement. The Soviets admitted last year that some of their "journalists" had met with ETA representatives in France.

The moderate Basque who were closely identified with Aguirre's pro American policies lost influence. Beitia contends that Aguirre died broken-hearted and bitter toward the United States in 1960, the year that President Eisenhower paid an official visit to Franco.

Others close to Aguirre dispute this, but the story is part of the lore that the younger generation of leaders has accepted from its elders.

Garaicoechea, 40, who epitomizes the new generation, said in an interview, "In the 1940s, when our leaders, Aguirre and company, were fighting for democracy against the fascists, they expected that the allies would be loyal with them. They were not . . . It's absolutely clear that there was a commitment. There is a moral debt, but we are not in the habit of presenting past due bills. We are confident that the United States is a great people and will not forget the Basques."

The greatest service Washington could render the Basques, said Garaicoechea, is to persuade the Madrid government to interpret the new Basque autonomy statute broadly to "give us real self-government." If Madrid insists on a narrow, literal interpretation, he said, then ETA's choice of violence will have been proven right. He estimated that 15 to 18 percent of the Basque favor violence.

An indication that even Garaicoechea's minimal demand of U.S. support in Madrid may be unrealistic came in the comment of a knowledgeable U.S. source that "the Basque IOU is on very yellow paper that no one else seems to have a record of." In any case, he said, "now, our first commitment is to the integrity of Spain."