AMAZON JOURNAL: DISPATCHES FROM A VANISHING FRONTIER.
By Geoffrey O'Connor.
378 pp. New York: Dutton.

The most appealing thing about ''Amazon Journal'' is that Geoffrey O'Connor does not claim to know everything or pretend that he fully understands what he reports. Indeed, if he arrived on the first of 10 trips to the region in 1987 with some preconceptions, these were soon worn away. Ten years later, he knows the Amazon better than many -- certainly better than most Brazilians -- but he has been humbled by its complexity. As a documentary filmmaker, O'Connor's task was to present his story in images. And he found them among distant Indian tribes, gun-toting landowners, dedicated Roman Catholic missionaries, poverty-driven gold miners, militant landless peasants and assorted victims of the violence endemic to the Amazon outback. Yet the more dramatic the images -- meaning the more salable to potential television clients in the United States -- the more he worried they were simplifying, even distorting, reality. So he decided to write his story. The book may well reach fewer people than his 1993 documentary, ''At the Edge of Conquest,'' which was nominated for an Academy Award, or even his new documentary, ''Amazon Journal.'' Yet it offers more. It not only recounts his own reactions to what he sees and hears in a strikingly honest way; it also analyzes the variables of greed, racism, hunger, sentimentality, adventure, idealism, violence and corruption that confuse how the Amazon is perceived.

It has always been a source of both magic and misery, drawing Portuguese ''conquistadors,'' explorers, scientists, traders and anthropologists long before Brazil's military Government decided to conquer the region with highways in the 1970's. The plan to colonize the Amazon with destitute peasants from the arid northeast failed abysmally. But today the destruction of primary forest, which began then, continues; Indian tribes and languages are disappearing; rare species of flora and fauna are threatened and rivers are being polluted by pesticides and mercury.

O'Connor is not an expert on Brazil, and he frequently laments his rudimentary grasp of the Portuguese language and his need to work through interpreters. Some small mistakes also creep into his accounts of recent Brazilian history. Yet being an outsider gives him a fresh eye: too often those ''speaking'' for the Amazon have their own narrow agendas, whether it is to protect the Indians, save souls, stop deforestation, rescue endangered species, develop Brazil's natural wealth or simply get rich. O'Connor raises questions without suggesting easy answers.

His approach is that of a reporter; he covered many of the Amazon stories that made news abroad during the five years leading up to the Earth Summit in Rio de Janeiro in 1992. It was a time when the Amazon was in vogue, when the burning rain forest was seen to be melting the polar icecaps, when the murder of the rubber-tappers' leader, Chico Mendes, created the first ''eco-martyr,'' when the British rock star Sting proclaimed the Indians to be his allies in saving the rain forest and, eventually, when world leaders traveled to Rio to make empty promises to protect the global environment. O'Connor was often ahead of the curve; he visited Mendes at his home in November 1988 and found a man who seemed resigned to death. When Mendes was murdered four weeks later, he might have been just another labor leader gunned down in a far corner of the Amazon. ''What distinguished Chico's death from those others was the time and place,'' he writes. ''The world was ready for -- indeed, desperately needed -- a human face to attach to the rain forest cause.''

Time and again, O'Connor is struck by how differently the Amazon is seen from the inside and from the outside. In the northern city of Boa Vista, a wealthy frontier boss tells him that the Yanomami Indians welcome the gifts of food and knives brought by the gold miners; in the Yanomami villages, he finds the Indians deeply resentful of the gold miners, who are polluting their land and rivers and chasing away wildlife. In Brasilia, the choice may appear to be between integrating the Indians into Brazilian society or preserving them as ''noble savages''; in the rain forest O'Connor finds the Indians eager to hold on to their customs, yet forced to come to terms with ''civilization.'' The author's eye -- his camera -- keeps him close to the ground, but he knows he must serve as a bridge between the Amazon and very distant television viewers. At times, the gap seems too wide: he wants to recount a complex process, such as the emergence of authentic Indian spokesmen, but news editors want shots of bodies. At other times, as with the Indian Woodstock that took place after Mendes's death, the world's news media, environmentalists and human rights activists show almost too much interest: ''I step off the stage and into a crowd of photographers. They are firing off shots at a dozen Kayapo warriors standing like stoics with war clubs and bows and arrows. The Indians pose compliantly in the direction of the photographers, who are eager to manipulate the Kayapo into the expected, sanctioned image of the native warrior.'' No less grotesque scenes occur at the World Conference of Indigenous Peoples paralleling the 1992 Earth Summit: ''For every indigenous leader here, there seem to be at least two or three photographers colliding, cursing, tripping and shoving, all of them trying to get the best angle. Given the current climate of interest in tropical forests, images of indigenous people are hot-ticket items.''

Once the Earth Summit was over, outside interest in the Amazon evaporated. But O'Connor kept returning and found the story ever more complicated. A new Government expelled most gold miners from the Yanomami reserve, but by then malaria was endemic. And some Kayapo, Sting's main allies in saving the rain forest, were themselves trafficking illegally in mahogany. During O'Connor's last trip to the Amazon, one incident became a metaphor for his whole experience. An Indian friend in a Yanomami village went hunting instead of showing up to be interviewed. ''My needs, my intentions, they're part of my world -- the white man's priorities,'' he mused with resignation. ''That's just the way it is. Conflicting agendas of disparate worlds. An old story. As old as that first encounter between whites and Indians on the shores of the Caribbean. Not one has ever been able to get around it. Not even me.''

Alan Riding, who headed The New York Times's bureau in Rio de Janeiro from 1984 to 1989, is now based in Paris as the paper's European cultural correspondent.