Amid signs that there is a serious effort by U.S. and Brazilian diplomats to smooth over sharp recent differences, Rosalynn Carter arrived here today and said she hopes her visit to Brazil will improve relations between the two countries.

In reply Brazil's foreign minister Antonio Azeredo da Silveria expressed "the pleassure and satisfaction the government and people have in receiving Mrs. Carter."

Sergio Arruda, spokesman for the Brazilian Foreign Ministry, confirmed what American officials traveling with Mrs. Carter have been saying - that behind the scenes the United States and Brazil have been seeking a rapprochement for several months.

He also confirmed that the United States has proposed an alternative to Brazil's plan to acquire from West Germany the capability to make its own enriched uranium and to reprocess used nuclear fuel.

The U.S. proposal calls for putting a reprocessing plant in a third country that would sell reprocessed fuel to other nations. The third country has not been selected, but Canada is one nation that has been suggested, sources here said.

The United States has opposed th Brazilian plan to get its own reprocessing capability because it wants to prevent the spread of plutonium, a by-product of reprocessed nuclear fuel. Plutonium can be used to make nuclear bombs.

Brazil, which imports 80 per cent of the oil it uses for energy, has aspirations of becoming a great power and wants to become independent of outside energy sources.

In January President Carter congerad the Brazilians by sending Vice President Walter F. Mondale to try to persuade West German Chancelor Helmut Schmidt to cancel the agreement it had made with Brazil in 1975 to provide the advanced nuclear technology.

Mondale's effort failed but Brazilian leaders were particularly distressed because he had talked to Schmidt without telling them. In their view, the discussion violated a memrandum of understanding that the United States signed in February 1976, saying the U.S. government would confer regularly with the Brazilian government on matters of mutual interest. The document was interpreted as giving Brazil a "special" relationship with the United Syayes.

Mrs. Carter's reception here was low-key in contrast to the elborate welcomes she has received in other countries that she has visited on her two-week, seven-nation tour of Latin America.

Arruda, the Foreign Ministry spokesman, said the reception was "normal," adding that "recent events point to a future that is very good for U.S. Brazilian relations."

While the dispute over the nuclear reprocessing plant was the major cause of the chilling of relations between the two large Western Hemisphere nations, human rights has been another thorny issue.

Brazil recently canceled a military aid pact with the United States and rejected $50 million in military credits because of a State Department report that described violations of human rights in Brazil.

Mrs. Carter will spend three days of her 13-day tour in Brazil, with a side trip Wednesday to the northwestern city Recife. She is to meet with President Ernesto Geisel Tuesday morning.

Associated Press reported the following:

Mrs. Carter arrived in Brazil as students were mobilizing for demonstration against the 13 year old military government.

In Brasilia, police raided the federal university for the second time in two weeks and some students were detained for questioning. Authorities said the university would be closed for three days.

Leaders of a strike that involved about 1,000 students of 9,500 at the unversity distributed an open letter to Mrs. Carter to the news media.

The letter, written in English, said, "We wish to emphasize that what is occuring here at the university of Brasilia is not an isolated incident, but a symptom of the oppression under which we, as students, have lived almost our entire lives - arbitary imprisonment and torture are fears that rule our lives. We sincerely hope that President Carter's policy toward Brazil will be guided by his support of those rights to which all human beings, everywhere, are entitled."