DIMALUO, China— The highest villages in the mountains above the Nu River seem to hang in the air. Farmers grow cabbage and corn nearly a quarter-mile up, as if cultivating ski slopes. Necessity has pushed them into the sky; land is precious along the river.

They may have to move higher still, perhaps into the clouds.

The Nu, which flows through a region that is home to old-growth forests, some 7,000 species of plants and 80 rare or endangered animal species, is the latest waterway coveted by a Chinese government that is planning to build a new generation of dams to help power its relentless, booming economy.

Unlike the Three Gorges Dam, the world's largest hydroelectric project and the subject of a bitter international debate, the Nu River plan has barely stirred a ripple outside China. But in China the project, which calls for 13 dams in all, has unexpectedly touched a nascent chord of environmental awareness and provoked rare public rifts within the government.

The reason is that the Nu is one of the last pristine rivers in one of the world's most polluted countries, running through a canyon region unlike any other, which a United Nations agency has designated a World Heritage Site. Last year, China's State Environmental Protection Agency and the Chinese Academy of Sciences publicly criticized the Nu project.

''If this river system is destroyed, it would be a terrible blow,'' said Li Bosheng, a prominent Chinese botanist. ''This area has been called the Grand Canyon of the Orient. It forms one of the world's most special canyon environments.''

For China, which already has more large dams than any other country, environmental awareness has been slowly growing since the long fight over the Three Gorges, where ground was broken a decade ago for a project that will cost at least $25 billion and displace more than a million people by the time it is finished in 2009.

No estimate has been made public for the cost of the Nu project. In Yunnan Province in southwest China, the Nu project would force the relocation of as many as 50,000 people, many descended from Lisu, Nu, Drung, Tibetan and other ethnic hill people. Many are farmers and herders who cannot speak Chinese and who choose to live on the land as their ancestors did.

''If people are forced to move around because of the projects, they are going to lose the way of life that makes them special,'' said one villager, Alou, an ethnic Tibetan. ''It's inevitable that people will lose their traditions if they move away.''

From its beginnings in the Tibetan high plateau, the Nu runs through one of China's most remote areas as it carves canyons through the rugged mountain ranges east of the Himalayas. It drops like a roller coaster, a descent of nearly a mile, plunging through gorges as the powerful current scrapes boulders white, as if with a steel brush.

Nor is it alone. It is in the family of rivers flowing out of the Tibetan plateau that become some of the most celebrated and important waterways in Asia: the Dulong, which becomes the Irrawaddy in Myanmar, formerly Burma; the Jinsha, which becomes the Yangtze; the Lancang, which turns into the Mekong in Southeast Asia; and the Nu, which becomes the Salween as it flows into Myanmar and along the border with Thailand.

China is moving to tighten its grip on many of these rivers. It has already drawn downstream protests for dam projects on the upper reaches of the Mekong. Plans are also under way to build several major new dams on the Jinsha nicknamed the ''Double Three Gorges'' because combined, they would generate twice as much power as the earlier project.

Opponents of the Nu project say their best chance may be to influence the project rather than to stop it. The political momentum to develop such projects in China is simply too powerful, particularly because China is facing a growing energy shortage.

The country is outstripping its power supply and suffering isolated blackouts and power shortages. It is also under heavy international pressure to shift from dirtier coal to cleaner energy sources.

But to critics, the government's answer to its energy problems -- developing the vast natural resources in China's west to power the economic boom in the east -- smacks of naked exploitation. Chinese environmentalists warn that China will have nowhere left unspoiled for future generations.

''The west development program has turned into the west destruction,'' said Wu Dengming, whose environmental group, the Chongqing Green Volunteer Union, collected 15,000 petition signatures opposing the Nu dams.

In early February, the switchback trails slicing up the mountains above the Nu in Yunnan were filled with villagers lugging pieces of roofing to mend their houses.

Village women washed their hair in the drainage ditch by the river, while a small boy used a bamboo pole to practice his calligraphy in the road. Many villagers still lived in huts built with strips of woven bamboo.

Hu Huashen lived in Yonglaga, a village of about 200 people on the coveted level land by the riverbank. He walked lightly down a concrete irrigation ditch, past wooden shacks built on stilts above pens of pigs and chickens, before stopping at a small tongue of land. He said that land, maybe three or four acres, allowed his village to survive.

''These fields may be flooded, and then we've got to move up in the hills,'' said Mr. Hu, a teacher. ''What can we plant up there?''