ONE personal experience can be worth a thousand studies in persuading a busy senator or Cabinet member to take a fresh look at an issue. That apparently is what led the tradition-minded, chemicals-oriented Department of Agriculture to do its first serious appraisal of organic farming.

During a trip to his home town, so the story goes, Secretary Bergland was visited by a neighbor who had switched from conventional chemical farming to organic farming six years before. He wanted Mr. Bergland to know that his soil had improved, crop yields had held up, production costs were down and his animals were healthier. Mr. Bergland was so impressed by the experience of a man he knew to be a conservative, successful farmer that he returned to Washington and ordered his agency to begin the study that has now just been published.

USDA had to start from the very beginning. How many organic farmers are there? And what is organic farming, anyway?Is it, the study concluded, a range of practices that minimize use of man-made fertilizers, pesticides, herbicides and animal feed additives. Instead, organic farmers rely on crop rotation, use of plant and animal fertilizers, and biological methods of controlling weeds and insects.

Most of these farmers previously farmed with conventional modern methods. The concerns that led them to switch included the rising costs of energy and therefore also of chemical fertilizers, a steady decline in the health and productivity of their soil, soil erosion, pollution of ground water by herbicides and pesticides, and the dangers these chemicals pose to their health and that of their livestock.

The study largely confirmed the experience of Secretary Bergland's neighbor. It found that most organic farmers are "highly skilled managers" with greater than usual knowledge of how to maintain soil productivity. Soil erosion, now a nationwide environmental worry, is much decreased. "Considerable quantities" of energy are saved because of cultivation techniques and greatly diminished use of chemical fertilizers. Though cash crop acreage is reduced because of crop rotation and the planting of soil-replenishing crops, production costs are also lower so that net income tends to be about the same.

It remains to be seen whether organic farming is a good solution for modern farmers. But USDA's first look suggests that organic farmers are developing workable alternatives to a number of troubling trends in American agriculture, including skyrocketing energy costs, accelerating soil erosion and every-ncreasing use of dangerous chemicals.