More than a thousand Brazillian writers, artists and other intellectuals have petitioned this country's authoritarian military regime to revoke laws that permit censorship, saying that otherwise "Brazil will soon be turned into a country that doesn't have much to say."

Signers include some of Brazil's best-known public figures: novelists Jorge Amado and Antonio Callado, composers Antonio Carlos Jobim and Chico Buarque de Holanda, architect Oscar Niemeyer and film-maker Nelson Pereira dos Santos.

Spokesmen for the signers say the petition had no direct connection with President Carter's stress on human rights, but they do say - without explaining why, specifically - that the climate for dialogue between the intellectual community here and the anti-Communist military regime is now favorable.

Carter's emphasis on democratic rule and human rights has, however, cought attention in Brazil, where the military has ruled with a heavy hand for the past 13 years. The Brazilian Press Association, which represents the media as well as individual journalists, just sent Carter a message applauding him for "reaffirming your commitment to defend human rights."

The American President has popped up in a satirical comic strip drawn by the popular cartoonist Henfil in Rio's widely read Jornal do Brasil. When one character kicks another, the victim warns: "You'd better stop bothering, or Carter's going to find out."

The aggressor - thinking in terms of Latin machismo rather than international politics, asks a friend: "This guy Carter - is he tough?" When the answer comes back "Very tough," he moans: "Uh-oh, I think I just roughed up his wife."

The very fact that the intellectuals' petition, the journalists' message to Carter and the Carter comic strip were published in the Brazilian press indicates some loosening - five years ago they would never have been permitted to appear in print or on the air. But President Ernesto Geisel, a retired army general, has given concrete signs of wanting to relax the military's grip on national life.

Perhaps more significant for the military regime here than the petition the message and the comic strip, signs of dissatisfaction are appearing in the Brazilian business community, which was among the strongest supporters of the 1964 coup that overthrew the country's last constitutional president, Joao Goulart.

In a statement extremely daring within the Brazilian contest, the head of the Sao Paulo Federation of Commerce, Jose Papa Jr., recently said, "The country must begin a move toward full democratic government."

When the businessmen backed the military takeover, he added, their ultimate aim was "a democratic regime" rather than what many businessmen see as unending and increasingly arbitrary hard-line rule.

Political observers here say the effects of Papa's statement are only beginning to be felt. Some say that the reason Commerce and Industry Minister Severo Gomes recently resigned - the first Cabinet change since Geisel assumed the presidency in 1974 - was that he sympathized with the businessmen's complaints but felt unable to do anything about them.

Still, the government shows no sighs of being ready to make any immediate changes. Justice Minister Armando Falcao, to whom the censorship petition was addressed, replied that he will continue, "firmly and serenely," to carry out the laws that justify censorship.

He also argued that Brazil's censorship is not as bad as people say. In 1976, he said, only 74 books were banned out of nearly 9,000 published; only 292 song lyrics failed to pass scrutiny of some 30,000 screened; only six movies were banned out of 4,740; and that only 29 plays were banned of 989 examined.

Ias Vomes, playwright and soap-opera author, was quoted as commenting that Falcao "is using numbers to deal with problems of the arts, as if they were economic problems."

"He says he banned only 29 plays," Gomes said. "Well, that's approximately the number of plays Shakespeare wrote."