By BRIAN HALWEIL

While the controversy over President Clinton's appearance at Tiananmen Square dominates the discussion of his visit to China, a more ominous issue is being ignored: China's water scarcity. This is a new security issue that could well emerge as a dominant force in China's future and the world's.

China is facing an impending water shortage that has the potential to undermine its food production, boost world grain prices and precipitate political instability in many developing countries.

The signs of water stress are everywhere. Half of China's 617 largest cities face water deficits. Beijing is among the most water-short, living on borrowed time as it takes irrigation water from farmers and over-pumps its ground-water supplies.

Satellite images show springs, lakes and rivers drying up throughout the northern haft of China. The Yellow River, the cradle of early Chinese civilization, failed to reach the sea for 226 days in ]997, leaving Shah-dong (a province that produces one-fifth of China's corn and one-seventh of its wheat) deprived of part of its irrigation water for several months.

A 1998 Chinese assessment reports that the water table under much of the North China Plain, a region responsible for nearly 40% of China's grain production, has fallen an average of 5 feet each of the last five years. A Sino-Japanese analysis from 1997 reports that water tables are falling almost everywhere in China where the land is fiat. Millions of farmers are finding their wells pumped dry.

China depends on irrigated land to produce 70% of the grain for its huge population of 1.2 billion people, but it is diverting more and more irrigation water to supply the needs of fast-growing cities and booming industries. As rivers run dry and aquifers are depleted, China's swelling demands for water are colliding with its limited supply.

The prospect of China turning to the global grain market to meet domestic shortfalls raises the possibility of jumps in world grain prices that could aggravate social and political instability in many Third World cities. With its booming economy and massive trade surpluses, China can survive its water shortages by simply importing more of its food. But low-income countries with growing grain deficits will struggle to pay the higher prices. For the 1.3 billion of the world's people who live on $1 a day or less, higher grain prices could quickly become life threatening. Hungry urban dwellers who lose patience with their governments will riot.

The problem is now so clearly linked to global security that the U.S. intelligence community has begun to monitor China's water situation with the kind of attention it once focused on Soviet military maneuvers. The National Intelligence Council, the umbrella over all U.S. intelligence agencies, has completed a comprehensive assessment of China's food prospect. The report, called the MEDEA Study on the Future of Chinese Agriculture, concludes that China's future grain shortfalls will result in "demands on the world grain market that approach today's total exports."

Mitigating China's water crisis will involve an across-the-board effort to restructure all sectors of China's economy with water-efficiency as a priority. Necessary steps will include raising the price of water to encourage efficient use in agriculture, homes and industry, strengthening pollution controls to protect scarce water supplies and shifting from water-intensive fossil fuel energy to water-efficient' solar and wind power.

Vice President Al Gore spearheaded efforts to get the U.S. intelligence community thinking about environmental issues and their ramifications for security. He has succeeded in broadening the definition of security to include such practical concerns as how future populations will be fed. President Clinton would be well advised to read this report and find time during the remainder of his visit to address China's growing water problem.

The president can pursue the MEDEA report's proposal for joint U.S.-China collaboration on water issues, as well as ask what else the United States and the world community can do to help solve the water problem before it escalates. A concerted and timely effort will benefit not only China, but also the rest of the world.