Three years ago, an international controversy swelled about reports that burning and bulldozing, especially on large cattle projects, had already destroyed a quarter of the Amazon forest. The dangers were extensive, some scientists argued, and closing in. This was the last major rain forest in the world, they said, and as such was one of the large reserves of the world's carbon.

If enough forest in Amazonia and elsewhere were destroyed, scientists warned, the carbon released into the air might warm the temperature of the globe enough to melt the polar icecaps and raise the ocean levels by as much as 30 feet.

"You will lose New York, Rio de Janeiro, London, Tokyo -- everything will be flooded," Henrique Bergamin, director of the National Institute for Amazon Research (INPA) said recently. "This is a little futurology, you know. But it is based on scientific fact."

From aerial satellite photographs that have recently been taken over the Amazon basin, it now appears that much less of the forest may have been destroyed. The numbers cited by scientists and government officials vary considerably, and there is dispute about the accuracy of the photographic interpretations and whether the whole large area being photographed can properly be called the Amazon forest.

But the most common figures estimate that 2 to 10 percent of the forest has been destroyed, although New York botanist Ghillean T. Prance, who has spent 18 years studying and working in Amazonia, still believes the correct figure is "over 20 percent, without any doubt."

"As far as I'm concerned, as an ecologist, that's basically irrelevant," said Judy Rankin, vice-director of INPA's ecology department, referring to the statistical dispute. "The secret of this whole deforestation problem is that the rate of deforestation appears to be exponential . . . . Exponential deforestation rates mean that the day you have half the Amazon, the next day you don't have any. That is a very difficult concept for people."

Even if the lowest figures are correct, deforestation has already begun to cause problems in some of the rivers and more populated parts of Amazonia. Fish may be having breeding problems because of denuded riverbanks that spill silt into the water and let direct sun heat river surfaces where once there was shade.

Floating material, which often grows from plant material discarded in forest cutting, has been seen recently along the northern Rio Negro in quantities Rankin called "astounding." It was deforestation-produced vegetation like this, with the chemical changes it caused as it decomposed, that helped kill the life in Lake Erie.

Scientists also worry that plant and animal species may be lost every time a large tract of forest is cleared. Of the thousands of species of bees in Amazonia, for example, only one pollenates the prized Brazil nut tree. That bee probably needs a dozen species of trees to make its own nectar.

With most tree species in Amazonia pollenated by animals or insects (in temperate zones wind carries much of the pollen), "you have this intricate, complicated set of interrelationships of all these huge numbers of species," said Thomas Lovejoy, science vice-president of the World Wildlife Fund in Washington. "It's true anywhere in the world that you can't take one species out without affecting the whole system, but it reaches its extreme in a tropical forest like the Amazon."

Climate is the other big worry. Scientists are convinced that half the rain that falls on the Amazon basin is generated by the forest itself, through evaporation and runoff. Replacing major hunks of the woods with other plants -- corn, for example, or pasture grasses -- would cut back the rainfall, but nobody is certain now just how much.

"We don't have a measure of that," said Lovejoy, who recently attended a Brazil scientists' conference on the rainfall question.

Besides, Bergamin observed, the forest uses enormous amounts of energy, presumably solar, to pump rainwater from the ground up through trees 100 feet tall.

"What will happen to this energy if you cut the forest?" Bergamin asked. "What will happen to the water? When you don't have this process, you probably will have floods when it rains, and dry season when it's not raining, because you don't have the buffer action of the forest."