The top State Department official for Latin America, Terence Todman, successfully weathered a conspicuously cool reception here in Brazil, where relations with the United States, are strained because of President Carter's positions on nuclear technology and human rights.

Todman, assistant secretary of state for inter-American affairs, is making his first official visit to South America as Carter's emissary. Brazilian authorities received him with a bare minimum of official courtesies, stopping only slightly short of what could be considered a snub.

The assistant secretary left Brasilia early today for Bolivia, his last stop before returning to Washington.

Once the closest of allies, Brazil and the United States have been drifting apart ever since Carter was elected President.

The government here is extremely upset over Carter's opposition to a sophisticated nuclear technology agreement Brazil signed with West Germany that will give the Brazilians the ability to make its own fuel for atomic reactors.

Brazil also regards a recent State Department report on human rights, which commented on the internal Brazilian situation, as "interference" in Brazilian affairs.

Todman's reception here contrasted sharply with those he got in the first two countries on his initnerary, Colombia and Venezuela, where he was warmly greeted by presidents. The head of Brazil's rightist military regime, President Ernesto Geisel, a retired army general, was not available to meet him. In fact, it was hinted that Todman was "lucky" to see even Brazil's foreign minister, Antonio Azeredo da Silveira.

The Rio newspaper O Globo said the Brazilian government gave Todman "cold treatment." Gazeta Mercantil, a financial newspaper, called Todman's reception here "more than discreet."

Todman's welcome was also noticeably colder than the one Brazil gave last year to then-Secretary of State Henry Kissinger, because under the Ford administration the United States had singled Brazil out for preferential treatment.

At a press conference in Brasilia Friday, Todman conceded, in effect, that the controversial Brazilian-West German deal is a fait accompli, declaring: "The United States considers Brazil and Germany to be sovereign nations that can sign any agreements they see fit." Both Brazil and West Germany say this nuclear know-how will be used exclusively for peaceful purposes.

Todman told reporters that the Carter administration will give preferential treatment to foreign countries that respect human rights, but added that the recent State Department human-rights report gave Brazil relatively higher marks than many other nations.

Todman also said that a Brazil-U.S. "memorandum of understanding" that was signed under Ford and Kissinger, giving Brazil special "consultant status" with Washington, will be maintained in principle.

There had been a general assumption here that because of Carter's seeming incompatibility with Brazil's nuclear policy and its human-rights situation, Washington had quietly shelved the memorandum.