On a few rice paddies in a noisy, ugly corner of this beautiful Chinese resort, an American scientist is working with Chinese colleagues on a Sino-American solution to future world food shortages.

Thomas Lumpkin, a researcher from the University of Hawaii at Manoa, has brought to Hangzhou the fruits of a worldwide search for a miraculous fern called azolla. The fern can provide a natural source of vital nitrogen to rice-growing soil.

Lumpkin is one of 40 U.S. researchers sent here by the U.S. Committee on Scholarly Communication with the People's Republic of China. It is an effort to win lasting benefits from the cooperation of two nations with a shared obsession with science.

Azolla, under the right conditions, can grow rapidly across the surface of rice paddy water to form a redgreen carpet. When the paddy is drained and the fern plowed into the soil, it provides a rich dose of nitrogen at two-thirds the cost of chemical fertilizers.

This is an ancient secret jealously protected by villages in Vietnam and some in China, which for centuries managed to market the fern to envious neighbors. But for the fern to become a useful tool, it must be kept alive thorugh the hot summers and cold winters -- a difficult task.

Lumpkin and the Chinese scientists of the Zhejiang Provincial Agricultural Science Academy are testing Chinese strains and the new varieties brought by him from other parts of the world, including the fruits of his own trek down the Nile in Sudan. They want to determine how the plant can best be used and maintained.

Azolla, which produces nitrogen through interaction with a variety of blue-green algae, is also referred to as "green manure." "It could be particularly useful in Bangladesh or central Thailand, places with a lot of standing water over a long time, Lumpkin said.

Although based in Hawaii, Lumpkin has pursued the mysteries of azolla over the world for years. He lives in a cramped hotel room here with his wife and their one-year-old son while he and the Chinese carefully gauge the different growing rates and resilience of the several different strains of azolla they are testing.

The plant is already used in taro fields in Hawaii and in cultivating some other crops in the United States, where government interest is high. The U.S. Agriculture Department funded Lumpkin's worldwide search for different strains of the plant, and the U.S. Agency for International Development is expected to support a special conference in Thailand to allow experts throughout Asia to compare notes on their work.

The Chinese and Vietnamese have found the plant needs a hot spring, preferably with high phosphorus content, to survive year-round. The Chinese have been using it for at least 200 years, often just as pig and chicken fodder.

But its fertilizing qualities have been long noted. An old legend said a fairy dropped the plant to earth as a gift to a young couple whose marriage was to be forbidden unless, by some miracle, they could greatly increase the rice yield in their village. "What is particularly unique about it is that it has a cumulative effect. The more you use it, year after year, the richer the soil gets," Lumpkin said.

The Chinese have spent about $60,000 on a special laboratory to house the azolla experiments, in a ramshackle, noisy part of town near an airbase. It includes a high wall and a live-in watchman, for the ferns are considered precious. There were reports that police had to stop agricultural officials from a neighboring province who were about to leave a recent conference on azolla with a number of samples picked up without authorization.

The researchers hope to discover ways to make the plant more resistant to insects and speed its growing time. Chinese harvests have been good in the last year, as they have in many other parts of Asia, but the Chinese economy is balanced far too precariously on chances of continued good luck with weather.

Peasants like the natural fertilizer, which does not add salts to the soil like many chemical fertilizers. If it works, it also offers the Chinese a way to increase their yields without opening more cropland in forest preserves and hillsides. The opening of such cropland has greatly aggravated China's erosion problem.