Once they had cooked up and tasted a mess of catfish in the test kitchens, there was no doubt what Department of Agriculture officials would do.

They decided to buy $2.5 million worth of catfish and give it away.

Farm-grown catfish is the newest goodie to make it onto the USDA's list of surplus foods eligible for distribution to charitable institutions, prisons and feeding programs for the elderly.

The catfish, you see, has left the low life of muddy creek bottoms and grown to respectability as a product of the American farm. And if it comes from a farm, USDA is almost always ready to lend a hand.

The department announced last week that it is spending $110,000 for 72,000 pounds of catfish for distribution by the Food and Nutrition Service. Before the end of the fiscal year, USDA plans to spend $2.5 million on catfish.

For the nonce, USDA won't be putting catfish in the school lunch program (there's a fear that fish bones may stick in tiny craws). But no matter. The catfish industry is licking its chops anyway, seeing the purchase program as almost as good as getting Uncle Sam involved in a promotion campaign to get more Americans to eat catfish.

While few people were paying attention, the catfish industry has been growing like blazes. Catfish farmers, mostly in the Deep South, have expanded production at an annual rate of about 25 percent during the last decade. Last year, they sold 72 million pounds to processors.

But they were raising more fish in their huge ponds than processors could handle and sell. Fish was stacking up in the freezers. So earlier this year, state officials and farmers from Mississippi began trawling for some federal help.

Mississippians in Congress encouraged USDA to take a close look and, sure enough, Washington took the bait. First, however, USDA had to decide how to pay for the fish.

Some officials wanted to use a fund that comes from import duties and tariffs. Part of the money is for fisheries research and development, but part of it stays under control of the secretary of agriculture. A confidential memo to Secretary John R. Block once described it as a "political slush fund," presumably because he can decide how to spend it.

Others argued against using the fund to buy the fish. Since catfish was in surplus, and since catfish farming was now recognized as farming in the real sense, USDA decided to use funds appropriated for surplus food purchases.

Not likely to be any squawks about that. Mississippians (Rep. Jamie L. Whitten and Sen. Thad Cochran) happen to chair the House and Senate Appropriations agriculture subcommittees.

After that it was easy. "We had some catfish sent in for testing," said Eddie F. Kimbrell, a USDA nutrition official. "It is really a good product. Catfish was in surplus and this purchase program represented a chance for an experiment."

As a result, the frozen, whole fish will soon be going to nursing homes, hospitals, soup kitchens and other feeding institutions that are more accustomed to receiving USDA's hamburger, pork and similar traditional surplus foodstuffs.

John Bode, a deputy assistant secretary of USDA, said, "We would have bought more if the schools could have handled it, but there was concern about bones in the fish. We felt schools would have to have filets, but they are too expensive."

That's just fine with the Catfish Farmers of America, a group of about 400 growers, based in Jackson, Miss. CFA thinks that now that protein-rich catfish is on the federal menu, there's no way USDA's constituents won't want more.

Mark Freeman, executive vice president of the CFA, added that the USDA purchase shouldn't be construed as another federal handout to a beleaguered industry. "This is not a bailout. Our people would strongly oppose a bailout," Freeman said. "But our problem is introducing our product. We look on this as a great help in putting the catfish in areas where we've never had it."