The two Kayapo Indians, their lank black hair falling nearly to their waists, had come down the Xingu River by boat with a westernized friend from the Juruna tribe. Now, all three was standing by the river bank, talking rapidly among themselves and watchings curiously as a white foreigner photographed this bustling Amazon boom to town.

"I am trying to explain to them how a camera works," said the young Juruna in broken Portuguese. "They have never seen one before."

Not all of Brazil's estimated 200,000 Indians live so remote from the ways of the "civilized" world. Many live on reservations maintained by the government's National Indian Foundation (Funai) for the express purpose of safeguarding the Indian as he is slowly tutored and gradually prepared for assimilation in Brazilian society.

But this situation may soon change. President Ernesto Geisel is expected to sign into law this month a government-prepared Indian Emancipation Decree that many anthropogists, missionaries and other experts charge would deprive the Indian of the protection and special status he currently enjoys and leave him open to exploitation.

Such an action would mark an abrupt turnabout in Brazil's attitude toward its indigenous community, which is estimated to have numbered more than 3 million when the first portuguese explorers arrived in the early 1500s. Although the full text of the new statute has not yet been made public, provisions permitting the "emancipation" of individuals or tribes through petition or government decree are already drawing heavy fire.

Interior Minister Mauricio Rangel Reis, author of the project, says, however, that the emancipation decree is part of a long-term project that will "amplify" the protection offered the Indian and enable him to "share all the rights an opportunities enjoyed by other Brazilian citizens." He also argues that to prevent Indians from disposing of tribal lands as they see fit would be to deprive the Indians of their "human rights."

But it is precisely the issue of protection of Indian land rights that has aroused the strongest criticism and debate. In both the Amazon and the Brazilian far west, the land frontier traditionally pushes forward a few miles further each year, leading to violent conflicts between settlers and Indians in which the Indians almost always emerge as the losers.

In some cases, such as that of a Kayapo tribe living in the region of Conceicao do Araguaia, 400 miles south of here, even peaceful contact with the Western world has led to disastrous results. A thriving community of 2,500 when first contacted in 1902, the Araguaia Kayapos had been reduced to less than a dozen by 1957.

"The Indian emancipation project is a structure for a clean form of genocide, without guns or poison," said Roman Catholic Bishop Tomaz Balbuino, president of the Interfaith Indigenous Missionary Council. "It is a criminal, murderous decree that will not only dirty the hands of those who have prepared it but will stain forever the national conscience."

"To emancipate Indian groups now," argued a group of prominent Brazilian anthropologists, ethnologists and sociologists in a recent joint statement, "would be to hand them over defenseless to infinitely more powerful forces, who sooner or later will snatch "the Indians land" for a pittance, either through claim-jumping or in repayment for debts, thus, absorbing [the Indians] as a source of cheap unskilled labor."

The proposed government measure is also opposed by the Indian leadership. Last week, two chiefs from the Xavante tribe, which has had perhaps the most contact with modern Brazil, went to Brasilia to tell the Funai president, Gen. Ismarth Araujo de Oliveira, that "we are not ready for emancipation.

"If our land is subject to invasion even while we are under tutelage," asked chief Aniceto, leader of a community of nearly 1,000 Xavantes, "what will happen to us when that protection ends?"

In Altamira, a dusty frontier town of 60,000 sandwiched between the Trans-Amazon Highway and the Xingu River, this clash between cultures is being acted out now in particularly dramatic fashion. A large agribusiness complex from the far south of Brazil, Cotrijui, has been authorized of clear and farm a million-acre plot skirting the Trans-Amazon Highway 75 miles west of here.

The Cotrijui plan calls for 2,000 families of farmers from southern Brazil to be settled in the area, with the first 200 families scheduled to arrive in December. Rich, black beans and corn will be raised for local consumption, cocoa beans, coffee and peppers will be exported.

But the lands in question are currently occupied by an estimated 200 Indians from the Arara tribe, who have resisted previous encroachments on their territory. Last year, the Araras were reported to have killed a white settler and two technicians from a state mining research company, and earlier this year they wounded with their bows and arrows a westernized Indian sent to try to talk them into moving elsewhere.

Official policy is that the Araras have priority and cannot be expelled against their will. But there is some popular resentment in town and talk of violence.

"If they don't clear out," predicted a pilot with long experience in the area, "someone will eventually drop 'bananas' on them" - sticks of dynamite tied together in a bunch.

In the far western Amazon territory of Rondonia, an area the size of West Germany, the problems are much the same. Funai officials in Porto Velho, the territorial capital, are trying to decide what can be done to remove 153 families of poor white squatters from Indian lands in the Aripuana National Park - where in 1971 Cintas Largas Indians killed two members of a Funai team.

"The emancipation of the Indian would be a catastrophe," said Funai regional delegate Delcio Vieira at his Porto Velho office as a young Indian in Jeans and T-shirt mopped the floor. "We don't want this to happen because the Indian will lose everything he has, including the thing most precious to him - his land."

Since the late 1960s, Rondonia has been the center of a tin mining boom that has turned Brazil into a leading tin producer. The territory's population has grown from 10,000 in 1970 to 600,000 now, and settlers continue to pour into the area to set up farms along the unpaved highway that serves as the only land link to the industrialized south.

The Rondonia region is home to "Indians in various stages of development, from the most pure and uncontacted to those who speak fluent Portguese," says Vieira. "But there is not one tribe here capable of making a decision to sell or lease their lands."

Individual Indians who have been assimilated into Brazilian society have also encountered difficulties with alcoholism and there are reports of Indian prostitution. Indian beggars can be found a long the river docks and in the streets of Porto Velho.

Funai officials are now planning a "campaign of attraction" to initiate contact with one of several tribes in the region that thus far have avoided Western civilization. At the same time, they are trying to attract once more a group of Zoros Indians who went back into the jungle less than a year after making their first contact.

"I almost prefer that they stay where they are," said Vieira. "The more isolated the Indian stays, the better off he is."