NOT VERY LONG AGO, countries on each of the world's seven continents, with the exception of Western Europe, could supply their own grain needs. Today only Australia/New Zealand and North America remain as grain suppliers--the others are importing larger and larger amounts of grain. The U.S. grain crop can spell the difference between hunger and sufficient food for hundreds of millions of people around the world.

The resulting pressures on American agriculture are at once welcome and dangerous. Agricultural exports are a major part of total U.S. exports. They have helped substantially to offset the country's immense bill for imported oil. And food exports could rise sharply in the next 20 years.

With more than one billion people suffering from hunger or malnutrition, this hardly seems the time to be thinking about limits. Yet ultimately the United States cannot meet the world demand for food. The effort to do so could not only sidetrack developing countries' efforts to build their own agricultural production, but also inflict lasting damage on the one domestic resource essential to agricultural productivity--the soil.

As demand grows, existing U.S. cropland is being farmed with greater intensity. To keep productivity up, farmers use more fertilizer and energy, increasing their costs. This in turn forces them to put cash crops on every available inch of land. Soil conservation practices--allowing the soil to "rest" and recover lost nutrients--become an unaffordable luxury. In parts of the United States, including some of the richest farm land, the resulting loss of topsoil has become critical.

Urban sprawl worsens the situation. As property taxes and land values climb, farmers lose their sense of the future. They "mine" the soil, squeezing out every possible dollar before selling out. Land that is best suited to farming is also often the most attractive to developers. This forces the remaining agricultural production onto land that is too steep or too dry. These problems are particularly severe in the arid West, where an area about the size of the original 13 states has been transformed to desert-like condition.

Finding a better balance between these conflicting pressures--the short-term advantage of larger exports, the longer range threat to a fragile resource, the immediate obligation to help alleviate hunger, and the longer range responsibility to promote agricultural production elsewhere--is a task that deserves more serious attention than it has so far received.