Argentine President Raul Alfonsin told Congress yesterday that a solution to the conflicts in Central America must be based on nonintervention by outside powers and respect by countries of the region for the rights of their own people and their neighbors.

Addressing a joint meeting of the House and Senate, Alfonsin made no mention of U.S. efforts to pressure Nicaragua through support of "contra" rebels fighting the leftist Sandinista government there. During welcoming ceremonies for Alfonsin at the White House Tuesday, President Reagan condemned the Sandinistas as "communists."

By contrast, Alfonsin appeared to be distancing himself from what many Latin Americans regard as excessive U.S. emphasis on military solutions in Central America. But his words also appeared to imply criticism of Cuba and the Soviet Union for attempting to sow discord in the region and of the Sandinistas for failing to permit democracy in Nicaragua.

Alfonsin, who became president last year after seven years of repressive military rule in Argentina, joined the other democratically elected, civilian presidents in Latin America by endorsing the "Contadora process" -- negotiations on a comprehensive peace agreement for Central America.

"My government supports the efforts of Contadora, which is the appropriate mechanism for finding stable solutions for the Central American countries," he said. The search for solutions, he added, should be based on these criteria:

* "The principle of self-determination as recognized by contemporary international law freely exercised through the will of the majority."

* "The existence of pluralistic democracies throughout the region."

* "The principles of territorial integrity and nonintervention should be respected and universally applied. This means they should not be invoked in a one-sided manner."

* "Specific warranties that the countries of the region will not meddle in the affairs of their neighbors."

* Elimination of "military mechanisms" or arms buildups in countries of the area that threaten neighboring nations' security.

U.S. officials said privately that they regarded Alfonsin's speech as reflecting the attitudes of most democratic governments in Latin America, and they said it was not inconsistent with Reagan administration policy toward Central America.

While acknowledging that Alfonsin would not endorse Reagan's call to support the contras, the officials noted that his main points -- support for Contadora, democratic pluralism and a halt to interference in the hemisphere by outside powers -- have also been advocated frequently by Reagan and Secretary of State George P. Shultz.

Alfonsin also said that the problems of Central America and the wider Latin American region stem from "generations of misrule," political and economic underdevelopment and chronic debt problems of countries trapped in the position of being producers of raw materials.

He acknowledged that his main aim in visiting Washington is to seek understanding for Argentina's struggle to arrest an 800 percent annual inflation rate and to repay a $48 billion foreign debt.

Argentine discontent about austerity measures demanded by the International Monetary Fund has created tension between the government and Argentina's creditors.

"That is why I request a special understanding from the senators and representatives meeting here and from the government of the United States," he said. "The principal purpose of my visit is to emphasize our common interest and adherence to democracy so that occasional misunderstandings and disagreements will not affect this basic fact."

Later at the National Press Club, Alfonsin complained that British Prime Minister Margaret Thatcher's "intransigence" is blocking Argentine efforts to negotiate a settlement of the Falkland Islands dispute that caused the two nations' 1982 war.

"I believe the United States could make her understand" the need for negotiations, Alfonsin said in response to questions about whether he was seeking U.S. help on the question.