SOME 4,000 farmers form 20 states and Canada, undeterred by snow-clogged roads, converged last month on the Ohio State Fairgrounds in Columbus for the 17th. annual Eastern States Draft Horse Sale. Before the day was over, 330 Belgian and Percheron horse weighing up to a ton had changed hands at prices ranging from $1,000 to $10,000.

Compared to the machinations of the protesting farmers in Washington, it was a low-key affair, not a media event. But it supplies part of the background that's missing as we puzzle over the tractor invasion.

The farmers at Columbus know something that the protestors have forgotten, or cannot go back to, in their debt-ridden commitment to agribusiness. They know that draft horses, nearly wiped out by tractors 30 years ago, are making a steady comeback -- in numbers, in prices, as show-stoppers and in terms of their economic uses on farms.

Most of the Columbus farmers, like those in Washington, depend on tractors and other machines -- but their dependence is not total. Typically, they run a "family farm" of 50 to 500 acres, the kind that for a generation has been bought up for urban development, conglomerated for agribusiness or simply abandoned under the onslaught of costly technologies and government policies which encourage them in the name of "efficiency."

On such farms, using horses is often cheaper in the long run than machines for a variety of operations. These farmers, whether from foresight or stubborness, have hung onto (or are returning to) big horses because they offer them a degree of self-sufficiency.

Credit to the Amish

NOTABLY, some 1,000 Amish farmers were at the Columbus sale. There are an estimated 60,000 to 100,000 Amish in the United States, and, in the stricter sects, they farm entirely with horses.

They are wonderfully "successful" farmers, working 50 to 150 acres. They provide a model of discipline and restraint at the opposite extreme from agribusiness, indeed from the whole syndrome of conspicuous consumption and keeping up with the Joneses. It is a model too stern for most of us, but there it is, haunting the brave, fearsome generalizations we and the tractor brigade have come to rely on.

The Amish deserve a fair share of the credit for the survival of heavy horses (they favor Belgians and Percherons), providing a market for the few diehard breeders who sweated out the conversion to machine power. These breeders were themselves small farmers who kept using horses alongside their tractors.

No one knows how amny thousand draft horses there are today, but it seems safe to say the number has doubled since the turning point about 15 years ago. The demand for them, in any case, far exceeds the supply. Advocates of Diversity

TWO AMIABLE missionaries, or prophets, of this small but lively counter-revolution were present at Columbus -- Maurice Telleen and Wendell Berry.

Telleen is the editor and publisher of the Draft Horse Jouranl, which in 15 years has built up to 18,000 subscribers, defining and energizing the heavy horse market. Two years ago he brought out a book, "The Draft Horse Primer" (Rodale Press), which has gone into a second printing.

Telleen finds time to farm 60 acres of his own near Waverly, Iowa, relying on horses. He doesn't waste time arguing for the abolition of tractors, certainly not on immense one-crop, unfenced spreads, but he is an eloquent advocate of horses on the smaller, diversified family farms.

His argument, in brief, is that a draft horse is "a source of power that reproduces itself, with good care is self-repairing, consumes home-grown fuel and contributes to the fertility of the soil." And is, besides, "spectacular."

Wendell Berry is a poet, novelist, former professor at the University of Kentucky -- and a small farmer. He is the author of a full-dress critique of government policies and exploitive technologies which have helped drive many millions of farmers from the land, under slogans proclaiming: "Food Is a Weapon."

The book, published in 1977 by the Sierra Club, is "The Unsettling of America: Culture and Agriculture." It argues that farming cannot safely be considered separately from the larger culture of America, that it must have limits and accept responsibilities. Therein -- although that is only a small part of the argument -- there is plenty of room for the economy of horse power.

Each bought a horse at the auction -- and went away to Iowa and Kentucky with a gleam in his eye. Many an Amish patriarch, and a host of stout, childblained farmers, made the same kind of investment in the survival of the family farm.