Chilean President Augusto Pinochet has agreed "in principle" with President Carter to allow United Nations human rights observers to enter Chile, according to sources close to Carter's ongoing talks with Latin American leaders.

The agreement is a major shift of Gen. Pinochet's 1975 decision to keep international human rights observers from investigating first-hand the charges of widespread torture and human rights abuse in his country. Carter referred obliquely to the agreement after his Tuesday evening discussion with Pinochet.

"We discussed the possibility of some observers who might go into Chile to observe what has been done there," he told reporters. "The observers would be from the U.N." The sources said yesterday that Pinochet had agreed to that in principle and the next move would be up to the United Nations.

The United Nations Commission on Human Rights sent a working group to South America in 1975, with Chile on the itinerary. The group was in Lima, Peru, when the Chilean government cancelled the invitation. The Organization of American States Human Rights Commission visit to Chile in 1974 was the last such trip by a major international investigatory body.

Sources in the State Department said Carter had been advised before his meetings with Pinochet and other rightist leaders to press for specific, overt actions showing increased attention to human rights. "We told him what had been done so far was mostly rhetoric," one official said.

In that connection, Carter said yesterday that El Salvador President Carlos Humberto Romero had agreed that "an inter-American human rights group" would go to El Salvador to probe charges of widespread violations there. Political turmoil and an upsurge in terrrorism followed a disputed election in El Salvador last February.

As expected, human rights have been a major topic in all the talks, which end today with visits to the White House by Argentine President Jorge Videla and Uruguayan president Aparicio Mendez. "He (Carter) has been encouraging them when he can," another State Department official said, "and for the others he's making it clear that whatever they hear from the military attaches, his own emphasis on human rights is serious."

Honduras ratified the Inter-American Human Rights Convention yesterday and the Domican Republic did so on Wednesday. "Things are progressing," sail an OAS delegate.

The Latin leaders have expressed their own feelings "quite strongly" on a number of issues besides human rights, according to knowledgeable visiting diplomats. Brazilian Vice President-Adalberto Pereira dos Santos and Colombian President Alfonso Lopex Michaelsen both criticized U.S. import controls on finished leather products, while proposed sugar import limitations drew fire from several Central American chiefs.

The talks themselves were "one of those things where nothing went as planned and everything turned out fine," one U.S. official said. Another official noted that the briefing books Carter consulted between meetings had been redrafted four to six times each to meet his demand that they detail every substantive issue between each country and the United States and among the countries themselves.

The visiting chiefs of state have been holding marathon bilateral meetings among themselves, quiet meetings that often would have been impossible to arrange at hom for political reasons. An example was the discussion at the OAS between the presidents of El Salvador and Honduras about a delicate border dispute over which neither country had been able to make the first move.

Argentine President Videla reportedly spoke with Venezuelan President Carlos Andres Perex Wednesday night on possible Venezuelan financial aid or investment, while Bolivian President Hugo Banzer Suarez was reported to be lobbying vigorously for an agreement with Chile and Peru to provide Bolivia an outlet to the Pacific Ocean.

"The real progress of the (bilateral) meetings will certainly rival the (Panama) Canal treaty in importance," a State Department official said.