By KATHERINE ELLISON Herald Foreign Staff

BRASILIA -- In this age of genetic mapping and space exploration, Sidney Possuelo devotes himself to tracking down people who have never seen a light bulb.

As the controversial director of Brazil's Department of Isolated Indians, Possuelo, 58, a thin, passionate man with a cloud of receding hair, has found eight such groups in the past 10 years. He spotted the most recent in April after a week of flying a small plane over the Amazon forest.

Little is known of these so-far-nameless people besides the shape of their straw-thatched dwellings -- about 15 long, narrow huts near the border with Peru -- and that, like most so-called ``lost tribes,'' they don't want to be found. If Possuelo has his way, nothing more will be known until they're ready.

``I have no plan to contact them. The plan is to protect them and leave them alone,'' he said, chain-smoking Marlboros at his desk, in front of a wall adorned with 32 tall, feathered spears.

Anthropologists suspect that the Amazon forest is the world's last refuge for native groups that have had few or no contacts with whites. The treatment of isolated Indians is an especially explosive political issue in Brazil, where vast areas remain undeveloped, but where loggers, miners, cattle ranchers and desperate subsistence farmers press relentlessly into the forest.

In a highly ambitious and much-delayed plan, Brazil's government has promised to set aside nearly 200 million acres, roughly 11 percent of the national territory, for its remaining 300,000 Indians. That includes 21 groups, discovered by Possuelo's department, who have had limited contacts with whites.

Development advocates say that is too much land for too few people, and they long for Brazil's old policy of trying to integrate Indians into society. Possuelo convinced the government to change its ways in 1989, when he created the department he now heads during a wave of public support for indigenous rights.

To protect the new group, near the Envira River in Acre State, Possuelo says he plans to station armed guards hired by Funai, Brazil's Indian agency, to close off river traffic to white settlers.

``The government isn't giving the Indians land; it is simply recognizing their rights to it,'' he says. ``It's not a matter of being nice. We have a historical and moral duty.''

Possuelo's job is not without its hazards. In the 37 years Possuelo has been working with Indians, he has faced malaria (contracted 36 times), the breakup of two marriages (casualties of his long stints in the jungle) and threatening encounters with fierce tribes. But the biggest threat has come from pro-development groups.

``I have nothing against him personally,'' said Euler Ribeiro, a right-wing federal congressman from Amazonas state who has been demanding that Posseulo be fired. ``But he's a liar, mentally ill, a demagogue and corrupt.''

Specifically, Ribeiro objected to Possuelo's policy of closing off rivers to whites. He also charged Possuelo with taking money from TV stations, although when asked for specifics, Ribeiro abruptly ended the interview.

Possuelo says he has never profited from his work, adding that his salary is less than $40,000 a year. He rents a modest home and drives a dusty VW Golf. His office is in one of Brasilia's shabbiest buildings, and he is continually wrangling for more government money for his expeditions.

As for Ribeiro, he said, ``He represents the forces that want to loot the Indians. Such people have no humanity in their proposals.''

Possuelo's work in recent years has won international recognition. In May, Spain awarded him the prestigious Bartolome de las Casas award.

At home, however, he is criticized even by his admirers.

Advocacy groups such as the Indianist Missionary Council, sponsored by the Catholic Church, found fault with Possuelo for making contact two years ago with a group of Korubo Indians in the Javari Valley. Possuelo said the contact was a rare exception from his policy of leaving such groups alone, but that it was necessary because of recent attacks on the Indians by loggers.

His purpose, he said, was simply to let the Korubos know they could count on the government's help, if needed, and to advise them of a Funai post about 40 miles away. But Roberto Liebgott, a director of the Indianist Missionary Council, called that contact harmful.

``He doesn't have the means to keep his promises of protection. And when you make contacts as he did with the Korubo, it automatically creates a kind of dependency that can leave serious scars. Worse, they can bring disease and open paths that others can follow -- others who don't have the Indians' best interest at heart.''

The Indians themselves have shown little gratitude for Possuelo's efforts. They've killed hundreds of Funai employees over the past few decades, and Possuelo himself was once held hostage for 23 days in the Xingu Park by tribe leaders negotiating for more land.

Late last year, the Korubos killed a Funai agent who had been Possuelo's friend and colleague for 17 years. Possuelo put up a cross in his honor. The Indians knocked it down. And just last month, Possuelo had to fly by army helicopter back to Acre State to rescue 21 Funai employees surrounded by members of the latest isolated group.

He maintains that such setbacks never make him angry or dim his zeal to explore the 34 other areas of the Amazon where isolated tribes may be living.

``Most people simply don't understand what isolated Indians are like,'' he said. ``They are persecuted, harassed, running from invaders. They have a lot more reasons to be intolerant of us than we have to be intolerant of them.''