Most small farmers do not do as well. The 223,000 farmers with sales of $20,000 to $40,000 earn profits on average of $4,900 a year. And when all 1.6 million small farmers are combined, their total farm earnings represent less than 1 percent of their family incomes.

In fact, with their second jobs, the Cogans match many larger farmers. The couple's total income of $45,000 a year or so, for example, equals the average for farms with sales of $100,000 to $250,000.

The trouble is, said Mrs. Cogan: ''I haven't seen any of it yet. So far, everything goes back into the farm. We take the livestock feed out of Chris's paycheck, so we don't see much of that. I don't see how farmers without a paycheck ever make it.''

The Cogans' outside jobs also make it easier to handle interest payments, which they say is their heaviest expense and which have proved to be the greatest burden of many full-time farmers. Rosy Predictions

Things looked much simpler shortly after the Cogans' marriage 11 years ago. Though he had grown up on a farm, Mr. Cogan was working in a foundry; Mrs. Cogan was employed in an office.

''Both of us always wanted to move back to the country and farm,'' he said. He also figured that if their dream came true, they might one day be earning less but enjoying it more.

''I figured I'd keep an outside job till we got the farm paid for - maybe in about 10 years - and then I could go to farming full time,'' Mr. Cogan said.