In remote, rural areas of China, a baffling and insidious disease has robbed millions of children of their health and left many permanently crippled.

Known as Kashin-Beck disease (KBD), after the Russian doctors who first identified it in Siberia in the 19th century, the ailment, according to World Health Organization estimates, afflicts as many as 2 million Chinese, and up to 30 million children risk developing it.

Li Changsheng, an environmental scientist and KBD researcher, recalls his first sight of its victims: "One morning, I saw peasants going to the fields. The way they moved, it did not look like walking, but more like dancing. As they came closer, I could see that they were hobbling on shortened and deformed limbs."

Anyone who has experienced the excruciating pain of an arthritic hand or shoulder will have some sense of the suffering of KBD victims, whose entire bodies sometimes are stricken with arthritis-like symptoms. Motivated by KBD's effects and its devastating potential, scientists in China and the Soviet Union have long sought its cause. Humanitarian concerns and the possible link to other forms of osteoarthritis have spurred more recent international research. Nevertheless, KBD continues to stymie medical science. "At this time," says Leon Sokoloff, professor of pathology at the State University of New York at Stony Brook and a leading KBD authority, "there is no conclusive evidence as to its origins."

Even so, years of observation confirm certain facts. KBD strikes primarily children and adolescents, whose bones are still developing; many live in mountain valleys with poor, loamy soil. Environment, not genetics, is believed crucial to the onset of KBD. "In China, people living in the countryside tend to eat food and drink water from their land, so it is easy to see the connection between environmental factors and Kashin-Beck," said Li, a former senior scientist with the Chinese National Environmental Protection Agency.

The link between the environment and KBD lends a bitter irony to a disease that strikes hardest at peasant families, who must live off the land. Chinese epidemiologists, working with local community health groups, have identified outbreaks in 13 provinces, a diagonal band from Manchuria in the northeast to the Tibetan plateau in the southwest. In many places, KBD has reached epidemic proportions; 90 percent of the inhabitants of some villages are affected. In the U.S.S.R., small pockets of the disease persist in eastern Siberia.

Clinical studies and X-ray analyses reveal a disease that progresses in stages. KBD often first appears in the spring in children ages 7 to 16, but some are as young as 4. Symptoms typical of arthritis -- pain, stiffness or swelling in the joints -- mark the early stage, which often is reversible if the victim leaves the disease area before serious damage occurs. Some types of hydrotherapy also have helped early-stage KBD.

If the disease is not checked, a generalized osteoarthritis sets in, with severe joint swelling. Later, as cartilage dies, joints may lock and bones may shift, shortening fingers. "In the fields," recounts Li, "victims' fingers are too short to hold farm tools the normal way, so they grasp the tools with their arms." By the final stage, the spine is bowed and the entire body noticeably shorter, especially in the arms and legs.

According to current medical understanding, KBD progresses as "a selective dying-off of the chondrocytes, or cartilage cells," says Sokoloff. Cartilage is found in two places: in the growth plate and on the cap that covers the end of a bone or joint. "The disease apparently attacks cartilage cells," he explains, "or it may attack small blood vessels that feed chondrocytes." Either way, cartilage cells die, blocking normal bone development, and, in the worst cases, causing severe skeletal deformities.

In searching for KBD's origins, most research has focused on three environmental factors, all related to diet: drinking water contaminated with organic waste, a deficiency of the mineral selenium or food grains tainted with mold. Each theory offers clues to the KBD riddle; none solves it.

One school of scientists from the Jilin Province Medical College, along with many rural Chinese, have long suspected the problem is caused by drinking water. "Water is more precious than bread," says Li, especially in the arid Loess Plateau region of northeastern China, where KBD is widespread. "People conserve water any way they can, so they dig channels and small ponds around their villages to capture rain water. Unfortunately, the run-off contains many organic wastes that gather in the ponds."

As plant wastes decay, they release humic and fulvic acids, byproducts of lignin, the woody element that binds the walls of plant cells. Ingesting the acids, some theorize, releases toxic compounds -- free radicals -- which damage developing cartilage cells by oxidizing fatty compounds in cell walls. Although research shows a correlation between drinking contaminated water and KBD, no proof exists as to how these acids might destroy human cartilage.

Other researchers, particularly those at Xian Medical University in Shaanxi Province, believe a chronic lack of selenium, an essential dietary element, triggers KBD. Although not fully understood, selenium helps to preserve body tissue elasticity and to improve blood and oxygen flow. Selenium tablets appeared very effective in preventing the disease among schoolchildren in Gansu Province. However, recent studies by Sokoloff cast doubt on these findings; his results fail to establish the value of selenium in protecting cell membranes.

In the 1940s, Soviet scientists began exploring the relationship between fungus on cereal grains and KBD. More recently, researchers at Harbin University in northeastern China have been investigating fusarium, a family of molds that grow on corn and wheat, the main dietary staples in KBD regions. Results indicate a link between wheat and corn consumption and KBD.

In this case, as in others, a link with KBD has not been established: A study from Sichuan Province shows that people who ate no wheat or corn also developed the disease.

The conflicting evidence makes many scientists suspect a multiplicity of factors. In the early 1980s, faculty at the Xian Medical University introduced a prevention program based on clean drinking water, improved hygiene and a variety of foods from different regions, including a high-protein, vitamin-enriched soup for elementary schoolchildren. After three years of this regimen, no new cases occurred.

A collaborative study led by Renate Kimbrough, a Washington physician, examined the importance of diet, especially protein, in preventing KBD. Results, published in August in the Journal of Toxicology and Environmental Health, indicate that disease-free inhabitants of Jilin Province consumed significantly more protein, in the form of rice, meat and eggs, than their disease-stricken neighbors.

As diet, hygiene, and living conditions improve, Kashin-Beck, like rickets, goiter and other environmental plagues of the past, may disappear before a cause can be identified. But while millions suffer and millions more remain at risk, scientists labor to increase international awareness and advance research.

Hope now rests on a 1987 agreement between UNICEF and the Chinese Ministry of Health. Under the plan, three Chinese medical schools will conduct epidemiological studies, each focusing on one of the major KBD theories. The plan's success rests on rigorous peer review and testing of the results; without it, foreign scientists will lack the hard, verifiable data needed to unlock the mystery of KBD.David Di Fiore is a policy analyst for the Environmental Protection Agency.