FOR decades, American farmers have ventured out beneath a blazing-blue sky in July, swept up a golden sea of wheat, and brought bread to a dependent world.
But this summer, the tillers of the earth's most bountiful soil are reaping the thinnest harvest of winter wheat in years. A cold wet spring has also hurt the corn crop.
The United States shortfall is the latest in a string of stingy harvests among the world's major wheat-producing nations. It coincides with a surge in consumption throughout Asia - particularly China - that has plunged the world's stockpiles of wheat and corn to their lowest levels on record.
The scant wheat harvest has sharpened the longstanding Malthusian debate over whether humankind has hit a limit in food production and must anticipate widespread famine.
At the least, agricultural diplomacy could change from a politics of surplus to one of scarcity. International tensions could rise, some analysts say, as the major grain-producing nations use their abundance as leverage against grain-scarce countries.
At the same time, three consecutive years of low, worldwide wheat and corn stocks suggest a long-term shift in the grain trade from a buyer's to a seller's market. Worldwide per capita grain production has fallen since 1983, according to the International Food Policy Research Institute (IFPRI).
Although the low stockpiles are worrisome, many economists contend that they do not foreshadow a global food crisis. To them, the dearth is an extreme dip in the usual rise and fall in grain production, rather than a fundamental market transformation.
''This is just part of the ebb and flow of agricultural output; it's certainly in line with what we've experienced within the last couple of decades,'' says Terry Francl, an economist with the American Farm Bureau Federation.
Yields should rebound in the next several months as the weather improves and higher prices induce more planting. In the long run, advances in technology and efficiency should help sustain grain supplies as a percentage of consumption.
''We may see a temporary reduction in the surpluses over the next year or so, but this will not signal a change in the long-term trends,'' says Per Pinstrup-Andersen, director-general of IFPRI in Washington.
Overall, worldwide grain production between 1990 and 2020 will grow annually 1.5 percent, a rate sufficient for raising the per capita supply of food, IFPRI cites.
For now, though, the contents of the world's bins are shrinking. The US winter wheat harvest is projected to be 8 percent less this year than in 1994. Global wheat stocks have fallen to a record low of 21 percent of consumption and should shrink further in the next year, according to estimates by the United States Department of Agriculture (USDA).
Drought and government mismanagement in several major wheat-producing countries are two reasons for the shortages. Also, the low worldwide stocks of coarse grains - corn, oats, sorghum, barley, and rye - will dwindle in the months ahead to an all-time low of 11.2 percent of consumption, the USDA says.
A myriad of factors will combine to keep grain stocks short of demand, say some analysts. First, humankind cannot expect to tap higher yields from the world's fisheries so it must turn increasingly to land-based sources of protein.
On land, however, the technology and increased efficiency that have significantly boosted grain production in the past three decades will lag behind population growth and the demand for a diet richer in protein.
Moreover, China has lost its status as a grain exporter and begun to look increasingly outward for its food. The world's most populous country will probably have to import 15 million tons of grain during the coming marketing year, according to the Worldwatch Institute in Washington. In 1993-94, China exported 8 million tons.
Water scarcity will depress grain production in many parts of the world. Soil erosion, pollution, and other forms of environmental degradation will impair harvests. Finally, the yield gains from the use of fertilizer are reaching a plateau.
''I don't for a minute mean to say we can't or won't increase production further. We will. But we will have a hard time keeping up with demand,'' says Lester Brown, president of the Worldwatch Institute.
Analysts who assert otherwise, he says, fail to recognize that production is ultimately constrained by the amount of water, land, and other finite resources.
For their part, optimists note that experts have sounded warnings of impending starvation for centuries. Yet food supplies have kept pace with demand, even between 1950 and 1988, when the world population more than doubled.
Biotechnology should impel advances in productivity well into the next century, analysts say. The ''Green Revolution'' will continue as the creation of high-yielding cereals, better irrigation, and expanded use of fertilizers and pesticides help buoy grain production, albeit at a slower rate than in previous decades.
Moreover, many farmers worldwide are far from reaching the upper limits of efficiency.
Most notably, grain output in Eastern Europe and the countries that comprised the former Soviet Union should rise dramatically as central planning wanes and growers respond increasingly to market forces, Mr. Pinstrup-Andersen says.
Indeed, the jump in grain production from the former socialist countries should balance out the otherwise destabilizing rise in demand in China, he says.
Power of prices
Most important, doubters of the future food supply underestimate the power of prices to invigorate production of grain and other foodstuffs.
''In this country and around the world, farmers tend to be very responsive to signals from the market,'' Mr. Francl says.
But all agree the debate over future food supplies must not obscure that malnutrition persists worldwide. ''We are not headed toward a major disaster,'' Pinstrup-Andersen says. ''The major disaster has been with us.''