A GIANT otter dives into a sluggish tropical river; a tree frog pauses on a branch: Televised images of the rain forest remind us that a uniquely valuable environment is disappearing. So we dig into our pockets for conservation efforts in other hemispheres, hoping our donations will stave off mass extinction and lessen global warming. But will they?Throughout Latin America, United States environmental groups and their supporters are rushing to build modern arks - parks and reserves that save pieces of the rain forest. But arks may not be enough to save the rain forest from the destitute settlers flooding it. In the words of one Peruvian environmentalist: "It's not just a question of trees. It's a question of poverty." Peru is a case in point. Colonists leave the Andean highlands to farm coffee, rice, and coca (for cocaine) in the Peruvian Amazon. Beneath the jungle's deceptively lush vegetation, they find poor soil and a harsh environment. Yet they keep coming. The profit motive, no doubt, drives the corporations and businessmen who deforest vast swathes of jungle for lumber, cattle, and agro-industry. But in many places the principal agents of destruction are colonists - desperate men and women who see the rain forests as their last hope. The Andean highlands, whence Peru's colonists flee, are the nation's poorest region. In 1984, less than half of the children there were adequately vaccinated or nourished. In Brazil's northeast and Bolivia's highlands, the picture is equally grim. Though people in the jungle are also poor, people move there from the more impoverished regions. During the 1970s, while Andean populations dropped, that of Madre de Dios, in southeastern Peru, grew 4.5 percent. The growth threatens Manu National Park, a UNESCO-designated "World Heritage Site" and one of the most biologically diverse places on Earth. Along with poor transportation, low agricultural prices, and lack of investment, highland poverty has an environmental cause: erosion and deforestation. Among the world's estimated 8 million "environmental refugees" are those who flee degraded lands and settle in the Amazon. The Andes are home to irreplaceable ecosystems. Lake Titicaca, for instance, on the border between Peru and Bolivia, is a vast freshwater sea 12,600 feet up, home to dozens of plant and animal species. Though much of the lake is a national park, there is little its tiny staff can do to protect it from impoverished local peasants eager to harvest its fish and wildfowl. Instead of trying to keep peasants out of the park, the rangers and the Peruvian Association for Nature Conservation (APECO) decided to work with them. Peasants now harvest "totora" reeds for cattle fodder and housing material, and patrol the park against poachers. Eventually, they will manage the lake's resources themselves, improving their lives and perhaps slowing emigration to the Amazon. At first, the program received support from US conservationists, but that support has been cut off. If Americans support parks in the Amazon while ignoring poverty in places like Titicaca, Latin America's parks may become unprotectable. First-world conservationists can do a lot to keep that from happening. They can share technical knowledge with South Americans working on reforestation, soil recovery, and environmentally sound development projects. They can provide financial, political, and technical backing to efforts like APECO's Titicaca project. They can see Latin American countries as whole entities, and not simply as rain forests with a nation attached. US environmentalists should tell Congress and the administration that we want aid for both rain-forest conservation and for the human beings whose poverty is seeding its destruction. Well-intentioned though it is, our interest in the rain forest won't save the Amazon. Helping the poor in places like the Peruvian Andes just might.