Small hydroelectric projects with generators the size of a suitcase can produce enough electricity to transform many isolated communities worldwide, according to the Worldwatch Institute.

In releasing a study on the future of hydropower, which now provides a quarter of the world's energy, the nonprofit research institute said the amount the worldwide water power could easily be quadrupled, eliminating the need for new coal or nuclear plants except in desert areas.

"Hydropower is a clean, renewable and inflation-proof energy source," said study author Daniel Duedney at a news conference. Norway, Ghana and Zambia already get 99 percent of their electricity from hydropower, and 32 more nations use it for more than two-thirds of their power, nearly all of if from large dams.

But because most rivers are publicly owned, the decision whether other nations' dam-building potential is realized is in their governments' hands, the study said, and they have often bungled the job.

Big dams cause big environmental problems of siltation, erosion, water borne disease and wildlife disruption, and if the problems are not anticipated, "disaster -- human and natural -- is sure to result," Duedney wrote.

The study, "Rivers of Power," said only 12 percent of Third World residents ahve electricity. In the People's Republic of China, 90,000 small-scale hydro units have been built since 1968.

Centered at small earthen dams and hand-built from local materials, they produce an average of 72 kilowatts "from generators the size of a large suitcase," Duedney said. That is enough to power a radio, a small refrigerator for antibiotics, a water pump and some lightbulbs.

Some larger units power small machines that husk rice, mill grains, make soap and produce leather and simple metal goods, and what is left over brings in movies, telecommunications and more lights.

"This creation of jobs in the villages has helped stem the exodus to already overcrowded cities," Duedney wrote, "and small hydro plants dramatically improve the quality of rural life by reducing backbreaking drudgery."

In some areas, paddle-wheel generating devices operate on barges parked in the middle of a river that cannot be dammed because of navigational or other reasons, the study said. Research to improve their efficiency is under way.

The study criticized international financial organiations, including the World Bank, for failing to invest much in small water power projects, charging them with ignoring the social and environmental costs of some mammoth dams now planned in Brazil, China and elsewhere.

Brazil's Itaipu dam will be the world's largest hydropower facility at 12,000 megawatts, while its Amazon River projects will flood an area the size of Montana.

In the United States, 3,000 small dams have been abandoned, mostly in the Northeast and Midwest. New laws requiring utilities to buy power from any producer, plus some financial incentives, have stimulated recovery of some of these dams, and applications for hydropower licenses quadrupled last year to more than 800.

Fewer than 3 percent of all U.S. dams are equipped to produce electricity, and putting generators at just the small ones could provide up to 24,000 megawatts, the study said.