SUDDENLY the morning air was split by an eerie howling. From their tree perches directly above us, three baboon-sized Indri lemurs let loose a barrage of screams that were answered by lemurs in other parts of the rain forest. A little while later, one by one, they sprang with giant leaps from tree to tree, ricocheting off trunks like billiard balls defying gravity, never touching the ground. After these short bursts through the forest, they stopped to rest on a branch, leisurely eating leaves and fruit.
Extinct for millions of years everywhere else in the world, lemurs now face increasing danger on this island refuge off the east coast of Africa. [A dwarf lemur, thought to be extinct even here, was found by a German biologist last year.]
The rain forests lemurs live in, also home to many plant and animal species found nowhere else, are fast falling to the axes of farmers seeking fresh cropland and fuel.
But the lemurs, an ancient relative of apes and humans, may be able to help save themselves - and their forests.
Fees paid by a small but steadily growing number of tourists to enter protected forests could help pay costs of forest guards and other measures to slow down forest destruction, according to conservationists and others.
``We're talking about a small, sophisticated, high-cost, high-value [tourist] market,'' says Christopher Ward, environmental officer for the World Bank in Madagascar.
``You have to be rather adventurous to come to a place like this,'' says Mr. Ward. ``But fortunately the people who are interested in biodiversity and interested in lemurs, and reptiles, and insects, and trees, and plants are, in fact, adventurous types.''
Madagascar is one of the richest nations in the world in terms of nature, but one of the poorest economically.
A World Bank analysis estimates that each tourist to Madagascar adds about $500 to the country's income. ``We hope some of those returns can actually be plowed back into conservation management,'' says Ward.
According to the World Bank, the number of tourists visiting this island nation increased from about 4,000 in 1985 to 28,000 in 1987, including about 8,000 who came specifically to see plants and wildlife.
Michel Rakotonirina, an official with Madagascar Airtours, a travel service, estimates that there were about 40,000 tourists last year, nearly half of whom came to see natural areas. The others, he says, came to enjoy Madagascar's many beautiful beaches and the related resort hotels.
In the Fort Dauphin area, exquisite beaches are reachable by air or a long overland trip. Once there, tourists can enjoy comfortable hotels and easy access to both desert and rain forest, where ring-tailed lemurs eat out of your hand.
Madagascar Airtours recommends a few trips, including rough hikes through rain forests, that are given mixed or negative reviews by some who have tried them.
``It was terrible,'' says Simone Mell, who, with a friend, made a five-day hike through one of Madagascar's most remote rain forests on the Masoala Peninsula. ``It was raining all the time. The way was very bad: You had to climb mountains all the time, up and down.''
Promoters point out that the trail passes through several villages. But Miss Mell says it wasn't pleasant. ``The villagers were very poor, and a bit unfriendly.''
Too many tourists, or an over-concentration in just a few forests, could result in crowds that would detract from the pleasure of a quiet encounter with lemurs or other natural attractions.
So far the Madagascar government has not spelled out how it plans to use revenues from tourists visiting protected forests.
Earlier this year, the government signed an agreement with the World Bank to increase the number of protected forests from the current 35 to 50 within the next five years.
At present, foreign funding from conservation groups and governments, including those of the United States, Switzerland, and West Germany, is pouring into Madagascar for various plans to save the forests. They include hiring and training guards, planting fast-growing trees that serve as alternative fuel sources, and establishing programs to help farmers improve production so they won't need to cut down forested areas to create additional cropland.
``Money is not a problem at the moment,'' says Olivier Langrand of the World Wide Fund for Nature office here. But, he says, ``maybe international [support] won't be like that within a few years,'' given the ups and downs of foreign assistance projects worldwide. Tourism revenue could make the difference in the long run.
There are challenges in developing nature tourism, says Baudouin de Marcken, director of the US Agency for International Development in Madagascar. ``You can't get to most places, and if you do, you can't find a place to stay,'' he says.
Mr. Rakotonirina says his country needs more four-wheel-drive vehicles, more hotels, and more roads.