XAPURI, BRAZIL, DEC. 11 -- The accused killers of ecologist and union leader Chico Mendes are set to go on trial here Wednesday, in a case that will focus new attention on the Amazon rain forest and the often deadly conflicts over how -- and by whom -- its wealth should be exploited.

The slaying two years ago of Mendes, who had won a United Nations prize for his work, helped galvanize worldwide concern about the fate of the Amazon. Internationally, he was seen by ecologists as a martyr to the greed of ranchers and loggers who seek to plunder the forest with their chain saws. Locally, he was seen as another victim of lawlessness and impunity on Brazil's wild-west frontier.

The men accused of killing him are Darly Alves da Silva, a local rancher, and his son Darcy. Mendes was despised by ranchers around Xapuri for his organizing of rural workers, including the rubber tappers, called seringueiros, whose livelihood depends on leaving the forest as it is.

A tiny courthouse here will be jammed Wednesday with reporters, television crews and a general hubbub the likes of which this riverside hamlet has never seen.

The larger issues involving the fate of the Amazon are not so clearly cast in fashionable green as initial coverage suggested. Studies have shown that less of the forest has been destroyed than previously feared. Officials see the main ecological problem not as the indiscriminate burnings that have received such attention in recent years, but rather the chemical poisons and social disarray brought to the Amazon by hordes of gold miners.

And despite a new attitude by the central authorities in Brasilia -- President Fernando Collor de Mello has named a top ecologist and longtime government critic as secretary of the environment -- officials are no closer to realizing a comprehensive strategy for the preservation and use of the Amazon than they were when Mendes died.

Mendes was killed at his home on the night of Dec. 22, 1988, and the suspects were arrested within weeks. It has taken two years to mount this trial, but as prosecutor Marcio Tomas Bastos noted, "By the standards of Brazilian justice, that's very quick."

Bastos said the prosecution will show that Darly Alves da Silva, 56, sent his 23-year-old son Darcy to kill Mendes. "I believe the proof is very solid," Bastos said this week.

Darly has consistently denied involvement. His son Darcy gave authorities a detailed confession, but the defense now claims the statement was made under duress.

Darly came to this remote town of 6,000 on the muddy Acre River after having been accused of violent crimes in several other states.

Violence is common in rural Brazil, and, according to union leaders and human rights activists, often goes unpunished.

"There have been thousands of assassinations," said Julio Barbosa, president of the National Council of Rubber Tappers. "This case will not show that Brazilian justice has changed. Brazilian justice is still working the way it always worked."

Sueli Aparecida Bellato, a legal adviser on rural violence to the national labor union CUT, said that while killings of rural workers and labor organizers have declined since Mendes's death, other forms of intimidation and violence have increased.

Mendes long had been under threat from local ranchers, who cut down large tracts of rain forest to make pasture for their cattle. Mendes battled them in the courts and with public pressure on behalf of landless rural workers, among them the thousands of rubber tappers who work the forest's widely spaced rubber trees in what ecologists hail as a perfect "extractive" use of the Amazon's resources -- taking a resource without resorting to deforestation.

The tappers and their leaders say rubber can still provide a viable livelihood. But the rubber booms that made bustling cities of backwaters like Xapuri at the turn of the century and again during World War II have long since ended. Plantations in places like Malaysia and even elsewhere in Brazil far outstrip the capacity and efficiency of the virgin forest, where the tappers laboriously harvest individual trees often widely spaced.

"We need the government to guarantee a price to the tapper so that at least he can earn the minimum wage," Barbosa said. "Now he earns less than half that much."

Mendes, the son of tappers, was the charismatic head of the Rural Workers' Union. He was also a dedicated socialist, another source of his unpopularity among the conservative ranchers.

Mendes' death sharpened the world's focus not just on the rubber tappers' plight, but also on the overall state of the Amazon Basin, which shelters by far the largest remaining rain forest. The slaying came at a time when ecologists were sounding the alarm about the annual burnings, when ranchers set the torch to big chunks of forest to clear them for pasture. Smoke from the fires sent up a thin pall of smoke that satellite photos showed covering much of the continent.

Claims were being made that an area of forest the size of Switzerland, or Belgium, or West Germany was being destroyed each year. Projections were cited indicating that in decades the entire forest would be gone, and claims by the Brazilian government to the contrary were dismissed.

But new satellite data, confirmed by both Brazilian and U.S. researchers, indicates that about 7 percent of the rain forest has been destroyed -- much less than some earlier claims. And the burnings have rapidly diminished during the last two years, to the point where Brazilian officials have come to see other problems as more pressing.

"A lot of what is being burned now has already been cleared," said Tania Munhoz, head of Brazilian Environmental Institute (IBAMA), the government agency charged with protecting the Amazon and the rest of the Brazilian wilderness. "Deforestation is way down this year, barely half of what it was last year. I would say the major problem is gold mining."

As many as 1 million men have left Brazil's crowded cities in recent years to search for gold in the Amazon's low hills and muddy waters. They use mercury to separate the gold from tailings, dumping tons of the poisonous metal into the watershed each year. They have brought disease that threatens to wipe out the few remaining native populations in the Amazon, like the Yanomami. And they live in rough, brawling communities where violence is the norm.

"It's much easier to control deforestation," said Munhoz. "The gold miners are so scattered, so mobile. They're here today, and tomorrow they're somewhere else." IBAMA is trying to do a census of the gold miners to learn the extent of the problem.

Under the overall direction of ecologist Jose Lutzenberger, whom Collor named as secretary of the environment in a widely hailed appointment, Brazil's policy has made a sharp turnaround -- in rhetoric, at least. Previous governments were seen as defensive and nationalistic, but under Lutzenberger the apparatus has come to welcome international concern and advice.

Critics charge, however, that Lutzenberger's attitudes have yet to translate into concrete policy changes that might in the long run make a difference.