The successful revolution in Nicaragua has jarred U.S. policy-makers into taking a fresh look at Latin America and seeking a new set of younger, more democratic allies there.

The fall of Nicaraguan dictator Anastasio Somoza, coupled with the demands of President Carter's human rights policy, have put on the defensive the military governments in the region that once knew they could count on U.S. support so long as they presented themselves as bulwarks against communism.

Carter's decision to send his wife Rosalynn and Secretary of State Cyrus Vance to Quito, Ecuador, to attend the inauguration of its newly elected civilian president, signaled Washington's intentions to cultivate what Vance called "a new generation coming onto the scene" in Latin America.

Even more significant was a friendly meeting Mrs. Carter and Vance held with three representatives of Nicaragua's new government.

"When I saw Mrs. Carter standing next to [guerrilla leader] Commander Zero for news photographs, I realized what a change it was," said one U.S. diplomat. "Can you imagine [former secretary of state] Henry Kissinger doing that, or Betty Ford with Mrs. Chamorro? It would never have happened in the Nixon or Ford administrations."

Violeta Chamorro, a member of Nicaragua's ruling junta, is the widow of a liberal newspaper publisher whose assassination touched off the civil war that led to Somoza's fall. She and Mrs. Carter spent six hours together at the inauguration ceremonies for Ecuadoran President Jaime Roldos.

In its attitude toward the new Nicaraguan government the United States appears to be trying to avoid the kind of hostility that some analysts say drove Cuban revolutionary leader Fidel Castro into an alliance with the Soviet Union after he won power in 1959.

During his two days in Quito, Vance discussed the situation in Nicaragua with the presidents and foreign ministers of nine Latin American countries, including the region's most important democracies.

A senior official on Vance's plane said the United States and Latin American nations all agreed to "support Nicaragua" and work together to provide three types of aid to the war-torn nation: immediate humanitarian relief, reconstruction aid and efforts to solve long-term problems. The Nicaraguans, the official said, "will determine the priorities" for the reconstruction of the country.

Although Vance met with foreign ministers of two countries with military governments - Argentina and Chile - it was clear that the emphasis of his trip was on consultations with democratic countries.

Particular importance was given to the five-nation Andean Pact, a South American trade group that recently has begun taking political action in concert.

Vance's longest meeting Saturday was with the foreign ministers of the Andean Pact nations - Bolivia, Peru, Ecuador, Venezuela and Colombia. All have democratic governments except Peru, which has scheduled elections for next year.

State Department spokesman Tom Reston said the "focal point" of the meeting was aid to Nicaragua, and the Andean Group would be involved in coordinating that aid.

A senior U.S. official said, "I think you will find them continuing to play an increasingly important role. They want to work together as a cohesive organization."

The Andean Group, which originated as a trade community within the Latin American Free Trade Association, did not begin to work together on political matters until its 10th anniversary summit meeting in Cartagena, Colombia, in May. It was the Nicaraguan civil war that spurred the organization to political activity.

The five presidents, shaken by the loss of life and widespread destruction in Nicaragua, approved a mutual declaration of concern. The foreign ministers of Colombia and Venezuela visited Nicaragua to present the declaration to Somoza.

Later the Andean Pact nations met in Caracas, Venezuela, and agreed on a joint position to present at a special meeting of the Organization of American States in June, called to consider the situation in Nicaragua.

The pact's position became the basis of the action taken at that meeting by the OAS, and it apparently was there that U.S. diplomats realized the group could be a useful ally.

At that meeting, the senior U.S. official said, "They were a constructive and positive force. They came in with a well thought out and unanimous position [that] made an important contribution to the OAS discussion."