An unlikely folk hero has emerged here as a champion of plain speaking and an enemy of bureaucratic doubletalk. He is Mario Juruna, 39, a chief of the Xavante Indian tribe, who - unlike most people in Brazil - refuses to be beated down by the official runaround.

The chief's words are being cited in newspapers and on television as pearls of logic succinctness. The Xavante leader, who wears a piece of bone through his ear and who comes from the remote western state of Mato Grosso, became a media figure as a result of a recent journey he made to Brasilia, the capital, to petition the government for supplies for his tribe.

Every time a government bureaucrat when into the "we're-doing-everything - possible" and "you-must-appreciate - our - position" routines, Juruna would whip out a tape recorder, to make sure he did not miss a word of what he was being told. Then the chief would carefully reply, many times using the Brazilian Portuguese slang expression "papo furado," which means "bulls - ."

An official in the Planalto Palace, Brazil's White House, branded Chief Juruna a "radical." The head of the federal Indian agency called him "tricky." But Brazilian news media see the straight-talking Indian as an illuminating example of an ordinary citizen rightfully seeking satisfaction from the government.

The Rio newspaper O Globo noted editorially that Juruna wouldn't have had to take a tape recorder to government offices were it not for the "climate of distrust" surrounding many Brazilian public officials. Jornal do Brasil, another important Rio paper, has taken to using the subheadlines "Juruna Understands" and "Juruna Does Not Understand" on news items dealing with official government pronouncements which make sense and those which do not.

Pasquim, a satirical weekly which often criticizes the authoritarian, military-run government here, splashed the Xavante chief's picture across its front page, with the caption: "The Brazilian who is right." This media exposure, in turn, has led to an incipient groundswell urging Juruna to go into politics.

Here are some examples of Chief Juruna's native wisdom:

Federal Indian agency official: "Am I correct in interferring that you're saying that the interior minister doesn't understand anything about Indians?"

Juruna: "But he doesn't. He's ignorant. He needs to learn about Indian customs."

Official: "But the minister does understand. He's there to help you. And he's helping me so I can help you."

Juruna: "I want the government to help Indians. I want the government to build schools and hospitals for Indians. The federal Indian agency is supposed to help Indians - not civil servants."

Official (upon being requested to provide ammunition for the Xavantes' hunting rifles): "I've told you over and over. We don't have the money."

Juruna: "Why?"

Official: "Because we don't."

Juruna: "Well, then the ammunition factory better close down. If there's no money for ammunition for Indians, there can't be any money for ammunition for the army and the police."

Official: "Besides, bullets are destructive."

Juruna: "That's right. They kill. But don't you think Indians should defend themselves?"

Official: "That's what the police are for."

Juruna: "The police only arrest poor people."

Although Chief Juruna maintained his pride and self-respect during his bureaucratic peregrination in Brasilia, he did not get the supplies - ammunition, blankets and boots - he originally had sought for his tribe.

Nor, despite an 8 1/2-hour wait in the Planalto Palace, did he get to talk to Brazil's President Ernesto Geisel, as he had hoped.

So Juruna set out for the long trip back to Mato Grosso. But he promised to return to Brasilia soon, to try once more to get the government to give him what he says the Xavantes need and want.

Meanwhile, Juruna's easily understood words live on in the overbureaucratized "civilized" part of Brazil. Newspapers are still reprinting what the chief said on his departure from the capital:

"In my tribe, anybody can talk to the chief. There is no bureaucracy. A man's word is his word. Here in the city, there is no such thing as a man's word. What there is, is 'papo furado.'"