"When something tastes very good, people think it must be very bad," Mr. Justumus said. "Even the French think this. And Americans. . . ." His voice trailed off, then rallied. "But a label that says, 'Eat foie gras, live longer'; what a marketing tool!"

The Gascon farmers are facing the threat of fattened livers from Eastern Europe. Last month a French television news program carried a report of a shipment of Eastern European foie gras that was hijacked in southwest France where it was to be processed. "Other countries can raise the ducks and geese cheaper," said Yves Saint-Pe, who fattens geese and ducks on his farm outside Auch.

Gascon farmers have also jabbed back at animal-rights advocates who contend that force-feeding ducks and geese to fatten their livers is cruel. Gesturing to the blue skies above her farm near Auch, Lucette Baron, who raises about 400 ducks and 150 geese a year, defended the practice. She said that before wild ducks and geese migrate, they stuff themselves, engorging their livers with fat to provide energy for the flight.

Mrs. Baron sees herself as the keeper of a holy tradition. "The Romans did this," she said. Walking into the barn to feed her flock, she was puzzled by the charge of cruelty. "My ducks don't run away from me," she said.

Mrs. Baron is the rare farmer's wife who keeps a small flock and, in the final three weeks of fattening, uses the traditional hose-necked funnel to pour corn directly into the birds' stomachs. Today, a typical foie gras producer raises 20,000 birds a year, favors ducks over geese (ducks fatten faster) and has an automatic feeding system. The 12,000 producers in Gers make more than a ton of foie gras a year, which can retail for as much as $25 an ounce.

And they think that in the work of Dr. Renaud they may have found the ultimate sword to defend their industry in a diet-conscious world.

"Eat Foie Gras for Health!" said Mr. Justumus jubilantly. In his office he is trying out slogans. "Even 10 years ago, you would have been laughed out of France for saying such a thing, but no one is laughing now."