This is a cowboy and Indian story, but not the usual one, because the cowboy is Marlon Brando and he's on the side of the Indians, several of whom are sitting around his hotel room here talking about their problems.

"Here comes Marlon with his feathers' - people think that all the time," Brando says.

In fact, Brando has been working on the Indian cause since 1955, when he says he read John Collier's book "Indians of the Americas," "and my head was twisted. I became an astounded American. I'd never been taught this in school. Hollywood had wrung our heads around. History had been rewritten by those folks on the coast."

Brando says this with a sense of outrage. He's becoming animated. "I'm getting cranked up," he says, and talks about how people thought, when he sent an Indian woman to accept the Academy Award for his acting in "The Godfather" in 1972, that all of a sudden Marlon Brando discovered A CAUSE.

"Hell yes, I'm sure as hell glad I did it," he says, speaking of the controversy surrounding that incident, "because for the first time an Indian spoke to 60 million Americans."

Without Marlon, the movement would still be two to three years away from where it is now in terms of exposure and recognition," says Russell Means, one of Brando's Indian friends from Pine Ridge, S.D., who's in Washington along with Brando and Dick Gregory and 5,000 native American Indians for "The Longest Walk."

The journey started on foot in California, and has come here to confront the nation ith some of the problems plaguing America's original citizens.

"It's a spiritual walk, a peaceful walk, something organized in relationship to our own spiritual beliefs," says Vernon Bellecourt, an Ojibwa Indian from northern Minnesota. "I say that for a reason. We once lived all around the Great Lakes, long before it was Minnesota."

"The word Indian is an idiotic word," says Brando. "Indians always called themselves 'the people.' It was Columbus who took the wrong subway and landed in America. He took the A train and landed in Flatbush. But he thought he was in India."

Brando doesn't come on like a godfather or a superman lending his flash temporarily to a trendy cause.

He sits curled up on a chair in baggy blue denims like a Buddha, listening intently to the tales being told by his friends. Occasionally he picks up a pad and makes notes, and replaces a cassette in a small tape recorder when it runs out. He fiddles with his watchband, an doesn't speak until spoken to.

"These gentlemen are articulate and intelligent, and can tell far better in chapter, verse and spades the anguish of their people," Brando says. "It's not my place. I do not represent their interests."

A word that crops up frequently in the conversation is genocide. "The first reason for the reservations was simple - 'out of sight, out of mind,' to perpetrate genocide," says Means. "What we want is liberation and freedom. There's been 110 million acres of land taken from the Indians. A 1969 government study showed the Indian people the fastest-growing ethnic group in America. Eight years later the population growth was less than zero. From 1971 to '75, 42 percent of our women of childbearing age had been sterilized, and not a whimper from the public. The U.S. pulled off the miracle of miracles, and managed to massacre our unborn."

Over 80 percent of our cases are documented by the GAO," (Government Accounting Office) Means says.

"I'm just living up to the policy set down by the government," says Brando. "Standing up for the liberty of people. We took our avowed enemies - the Nazis - and brought them to their knees and then rebuilt them and then commuted their sentences. These people only want a fair deal. No Indians expect the Pinta and the Santa Maria to sail up the Hudson and we'll all get on and go back to Minsk and Dublin. One would hope that the American government would have the insight to realize that the American Indian is not going to lie down and repudiate his culture and say, 'Okay, I'll go to work at Needick's or Chock Full 'o Nuts.' It's like an echo in a sewer pipe. Carter sends Mondale out to preach about human dignity. The American Indian's health is in danger. They're going to laugh themselves to death when they read it."

"We wrote to Carter before the election," says Bellecourt," and he responded. 'We must honor and implement our treaty obligations to the American Indians.'

"But basically the Carter administration has ignored us," adds Means. "The anti-Indian policies of the government have accelerated.

"Indians are thrown in jail in South Dakota and Mr. Vance doesn't go to speak with them," says Brando. "But I don't blame the American people for not understanding. It doesn't mean much until you're in a basement and you see Indians bleeding and doctors pulling out bullets, like I did in Gresham. Wis. I mean, I've never seen bullets flying around, but they were coming from two directions."

Although Brando says he dislikes "having cameras shoved in my face [and people] asking me about Indians," he has become - perhaps by default - the most recognized spokesman for the cause. ABC-TV has realized this enough togive him $100,000 in seed money to develop a 14-part series that will show the other side of the Indian story. The docu-drama series will include three documentary programs and 11 dramatic shows, with Brando playing the role of a colonel responsible of the Sand Creek Massacre and the slaughter of the Cheyenne.

"Hollywood has done more damage to Indians," says Brando.

"The bread and butter of the movie industry has always been the killing of Indians. They always depict them as the bad, ferocious wild Indians, and the Indian girl in love with the soldier who turns on her people. It makes you want to - - - on your leg."

Brando says he's totally perplexed at how to get the American public to pay attention to the Indians. At the same time, he says he's baffled by people's interest in his private matters.

"I spent four hours talking with the staid, dignified English press about the Indians, and they wound up writing about how much money I made on "Superman." My personal life is nobody's business. It's not pertinent. It's dull. I don'want to know how you make love to your wife."