FARM POLICY is due for another overhaul.

As Agriculture Secretary John Block describes on the opposite page, the administration hopes to use the 1985 farm bill to reduce government interference in agricultural markets and cut the high cost of farm-support programs. That will be a tough fight, but prospects for success will be improved by a frank recognition on all sides of the changed state of U.S. agriculture.

Even the most die-hard supporter of farm-subsidy programs would be hard-pressed to say they are working well. Despite record government outlays, farmers are plagued by big debts, high interest rates, weak prices, dwindling export markets and falling land prices. Thousands of farmers face foreclosures in the coming months, and bank failures in rural ares are already at post-Depression highs. While failing to support farm incomes, government programs have also built up costly surpluses and promoted over-intensive farming and soil erosion. Quite a record.

There will always be a role for government programs that provide some measure of stability to the naturally erratic farm market. But by reducing target prices, crop loan levels and total support payments to any farmer, the administration hopes to let market forces play the major role in determining future crop supply and demand. Other factors besides efficiency, however, have provided the rationale for this country's farm programs, and they need to be reckoned with in any policy overhaul.

Nostalgia for the family farm continues to be a major theme not only in the movies but on the floor of Congress. Jessica Lange, Sam Shepard, Sally Field, Mel Gibson and Sissy Spacek battle the banks, the elements and the inroads of technology on the silver screen, and congressmen invoke their image as thy seek to reauthorize programs the benefits of which flow to an entirely different sort of farmer -- one whose business is run on a large scale using the most modern agricultural and accounting technology.

The largest 12 percent of farms -- those with yearly sales of more than $100,000 -- now receive close to half of all farm subsidies and account for the major part of all farm sales. Medium-sized farms still contribute much of the country's food supply, but their number is dwindling. Unless Jessica, Sam, Sally, Mel and Sissy can find part-time jobs in a nearby town, or a specialty niche in the farm market, neither current farm-support programs nor a return to more open markets will likely keep them down on the farm.

Congress may well decide that it doesn't want to embrace the more closely targeted or intrusive programs that would be needed to save the small and middle-sized farms. At least it ought to stop justifying current policies on that basis.