MANAUS, Brazil (AP) _ A popular belief about the Amazon is that it is the ''green lung'' providing much of the world's oxygen. Another is that it is a jungle.

Neither is true, Brazilian experts say.

Paulo de Tarso Alvim, one of Brazil's leading plant physiologists and researchers, debunks the ''green lung'' concept, which holds that if anything happens to the Amazon the world will suffer a loss of oxygen.

''That is enirely groundless, because the Amazon uses as much oxygen as it produces,'' he says.

Through the decay and oxidation of its own dead matter, the Amazon consumes as it produces through the process of photosynthesis, he explains.

The felling of trees in the Amazon, however, does contribute to an increase of carbon dioxide in the atmosphere, although probably not as much as cars and industry. Alvim says deforestation in the Amazon is responsible for only 1 percent of the carbon increase.

It also is often said that Amazon deforestation is changing the world's climate.

''Maybe it could change the weather if the entire Amazon was destroyed,'' says Alvim. ''But there is no clear scientific data that it does so now. It is pure speculation.''

The Brazilians do not call the Amazon a jungle. They refer to it as a ''mata,'' Portuguese for woods or forest. The Brazilian Amazon is mostly tropical rain forest.

Because little sunlight filters through the trees, most of the Amazonian ground is generally clear of undergrowth.

A person can easily walk through the rain forest on a thin layer of moist, decomposing leaves, which provide the nutrients for the trees.

Some trees grow a high as 100 to 150 feet as they compete with each other for sunlight. The trees in turn become a habitat for wildlife.

Angelo Augusto dos Santos, who heads the Ecology Department at the Amazon Research Institute in Manaus, said calling the Amazon a jungle ''encourages its taming and conquest.''