Brazil today delivered a lengthy official blast at "sensationalism" and "politicization" of the human rights issue in a speech obviously aimed at the United States and its support of international investigation of accused rights violators.

Without mentioning names, Brazilian Foreign Minister Antonio F. Areredo da Silzeira, told a closed meeting of the Organization of American States that the issue was obviously being used for "achieving ends other than the intrinsic protection of the rights of man."

In a later OAS session this afternoon, U.S. Secretary of State Cyrus Vance said that a U.S. agreement with Panama on a new canal treaty may be reached "before the end of the summer." Recently the United States has indicated that a new treaty was expected by the end of June.

Both Vance and Panamanian Foreign Minister Nicolas Gonzalez Revilla described difficult economic issues still remaining between the two countries.

Except for the canal statements, this year's OAS General Assembly has concentrated almost exclusively on the subject of human rights. In a speech yesterday, the most severe yet delivered by the Carter administration on human rights, Vance told 25 OAS member nations that there can be no "ambiguity" about their commitment to observance of such rights for their citizens.

Brazilian Foreign Minister Silveira spoke today of a "pseudo-investigatory preoccupation" with human rights, and warned that "inquisitorial" attitudes can "degenerate into attitudes of pure interference in the internal affairs of another country."

In a private lunch following his address, Silveira and Vance spoke almost exclusively about the rights issue according to a State Department official traveling with Vance. "It was a very frank discussion - and that term carries with it all the appropriate diplomatic baggage," the official said implying that the two reiterated their strong stands.

Vance's speech on human rights has provoked an enormous response at the conference which began yesterday. All the foreign ministers have addressed themselves to the issue in their speeches, endorsing or opposing the U.S. view. That view, as expressed by both Carter and Vance, includes giving the OAS Human Rights Commission more power to investigate charges of violations by member countries.

"There is no confidence in Carter in my country," one member of the Argentine delegation said. "We sincerely believe that he is far too much to the left in his dealings with the Soviet Union."

Argentina has no intention of weakening its internal security by bowing to Carter's demands, he said. "What we need more than anything is time," the diplomat said. He said Argentina believes it will have wiped out all terrorist guerrillas by the end of this year.

Argentina, Brazil and Chile are among the several Latin American countries that have been accused by other international human rights organizations of political imprisonment and torture of its citizens.

Foreign Minister Silveira's criticism of the U.S. campaign on human rights today echoed stands taken yesterday by Argentina and Chile. In a private 40-minute conversation with Vance this afternoon. Chilean Foreign Minister Patricio Carvahal spoke only about human rights, a U.S. official said. He said Carvahal repeated parts of his speech yesterday in which he justified his country's policy because of an international "Marxist-Leninist" subversive conspiracy directed by Moscow.

The U.S. official said some Latins have accused Washington of not understanding their situation. Many diplomats say that Latin officials retain the attitudes of the Cold War, during which they were supported by previous U.S. administrations and the CIA. They now feel they are being deserted by Carter, the diplomats say.

In other speeches yesterday and today, Costa Rica, Mexico, Peru, Ecuador and Venezuela have supported the United States on human rights. Vance's private meetings with each foreign minister, ranging from 25 minutes for Haiti to a two-hour dinner last night with Venezuela, are in part intended to take "soundings" for a possible human rights resolution.

Such a resolution, U.S. officials have said, will contain a concession to the threat of international Communist subversion by denouncing terrorism.