POKOINNY BAY, Eastern Siberia -- A massive brown bear, hungry after a long winter sleep, loped with surprising speed across steep meadowland rising from the world's oldest and deepest lake. In a clearing below, three noble red deer froze, and then disappeared into the pine forest. These were the most visible denizens, on a frosty May morning, of the Baikalo-Lensky nature reserve in Eastern Siberia. They are a tiny part of Russia's vast natural treasure, a wilderness as rich and vital to the earth as the Amazon rainforest ? and equally threatened. While the Soviet Union justly earned a reputation as a monstrous despoiler of the environment, it also protected a unique network of nature reserves ranging from the Central Asian desert to the Arctic tundra. These 170 reserves were totally off-limits to visitors and they sheltered a bewildering variety of plant and animal species. Now, with economic collapse and a breakdown of central authority, the reserves stand exposed. Poachers and loggers, prospectors and ranchers are gnawing away at Russia's natural heritage. The "green" movement is moribund, the profit motive is exalted and the few naturalists seeking to defend the reserves are virtually powerless. "Everything is beginning to break up and fall apart," said Vladimir Krever, the World Wildlife Fund's representative in Moscow. Russia alone has 85 of the reserves, enclosing as much territory as all of Italy, as well as 88 semi-protected national parks and wildlife refuges with even more space. But scientists have warned that their deterioration could destroy the world's largest temperate forest, an essential defense against global warming, and hasten the extinction of thousands of unique species, from the Siberian tiger to Lake Baikal's unique freshwater seals. "The vast landscapes of the Russian Federation represent one of the last opportunities on Earth to conserve relatively intact ecosystems large enough to allow ecological processes and wildlife populations to fluctuate naturally," the World Wildlife Fund said in a report earlier this year. Here in the Baikal region, park rangers who earn less than $20 a month often turn to poaching to support themselves. More honest employees have no jeeps or walkie-talkies to patrol their vast territories against the incursions of hungry locals or criminal bands of hunters. Local authorities, emboldened by Moscow's decline, grab chunks of protected land for grazing or to build new vacation lodges. The government can no longer pay for the aircraft that used to deliver supplies and fight fires. The reserves are fighting back as best they can, seeking aid from the West and allies within Russia. Many have recognized their total isolation was possible only in a totalitarian regime and that they have to allow some access, both to raise funds and to win local support. Breaking with eight decades of strict policy, the Baikalo-Lensky reserve has mapped three routes through its vast territory, hoping to attract adventurers and "eco-tourists" from the United States. The neighboring Pribaikalsky National Park has formed a small furniture-trading company, seeking profits that could increase rangers' salaries or buy equipment. The Institute of Limnology, a longtime leader in the fight to save the lake from industrial polluters and once a proud cog in the powerful Soviet Academy of Sciences, now markets Baikal Water in plastic bottles labeled in Japanese and English.Yet many fear that, without urgent help, they will not save the lake, the woods and steppe around it. "I have to say that perestroika has brought us nothing good," said Alexander Zayatz, director of the Baikalo-Lensky reserve. "We suffer from a fever of instability." Lake Baikal has long attracted the interest of Russian and Western environmentalists. In 1916, Tsar Nicholas II created Russia's first reserve on Baikal's eastern shore to protect the fur-bearing sable, which had been hunted almost to extinction. A half-century later, when authorities built a giant cellulose factory on Baikal's southern shore, the Soviet "green" movement was born. Today, the region boasts three reserves and three national parks. But despite all the attention, Baikal today offers a vivid picture of the problems confronting nature preservation throughout Russia. The cellulose plant is still operating despite years of campaigns and promises, and looming unemployment in the Irkutsk industrial basin makes closure unlikely. The "greens" who fought against the plant and other factories to the east that pollute Baikal's watershed and those to the west that pollute its air, have all but faded away. "People start to forget about Baikal, and think more about how just to survive," said Zayatz. Emboldened by the weakening of Moscow's authority, a collective farm on the preserve's northern border has grabbed 1,109 acres of northern steppe, where several rare plant species grow, to graze cattle, Zayatz said. "We could stop them by closing off one road," he added. "But we don't have the manpower, transport or communications." In an unresolved conflict, the powerful local energy company is battling for a piece of shoreline inside the national park to build a vacation home for its big shots. The company won local support by promising to extend electricity to several remote villages -- but only if the national park gave way. Poachers trespass to shoot bear and the diminutive musk deer, whose glands are valued by Chinese medicine makers. At the best hunting spots, poachers have burned down ranger cabins to make sure no one interferes, officials said. Some of the hunters are part of commercial gangs. "Poaching has become big business," said Amirkhan Amirkhanov, deputy minister of the environment. "The gangs have carbines, while our wardens have weapons going back to World War II." But many hunters are local inhabitants trying to survive. Overfishing has eliminated the livelihoods of many, as the population of the lake's unique omul fish declined below commercial levels. At the same time, the creation of the Pribaikalsky National Park, in 1986, and the reserve, in 1987, ruled out logging, gold mining and guiding foreigners on hunting excursions, while generating considerable hostility. Forest rangers such as Vladimir and Natalya Ignashev, living in a wind-buffeted log cabin on Kadilny Bay, have few resources to block poachers. They know they would do better to enlist the locals than to fight them. By encouraging tourism, they hope to give everyone a stake in preserving the wildlife that would attract visitors. Russia's economic slump in one sense has given the naturalists some breathing space. Fewer boaters than in the past can afford gasoline to roar around the lake; most enterprises can only dream of building hotels; new factories are out of the question. Baikal's water is so clear that from a high cliff it is still possible with binoculars to watch fish swimming lazily along the sandy lake bottom near the shore.