Jean Troigros, the lion of Roanne, was on the prowl in the Georgetown Market last Wednesday when he spotted something familiar.

"Oseille . . . Sorrel," he said, a smile appearing from the depths of his well-trimmed gray beard. "Can we find some salmon?" The salmon was only a block away, at Cannon's Sea Food, so Troisgros had the basic ingredients for what may be the most famous restaurant in France: Escalopes de saumon al'oseille Troisgros.

Jean Troisgros and his brother, Pierre, both chefs and both former students of the great master Fernand Point, put the small city of Roanne on the culinary map a decade ago when the restaurant bearing their family name won the top, three-star rating in the Guide Michelin. The Troisgros have been leading innovators of nouvelle cuisine and to some gastronomes their culinary creations have even surpassed those of Paul Bocuse, their neighbor and friend in nearby Lyon.

Troisgros was here to demonstrate at the International Wine and Cheese Festival sponsored by the Maitres des Tastevin. He shopped quickly, but with keen interest. A box of fresh basil caught his eye at one stand. He jumped behind the counter at another to show the butcher how he wanted a piece of veal sliced. He tasted some homemade creme fraiche at the dairy counter, then tasted it again. "It's good," he said with a grin.

There was talk of kiwi fruit, which, he said, is now being grown in the south of France near Toulouse: a search for the English word for the leafy vegetable blette (chard) and a rapid grab for some fresh tarragon.

At Cannon's Troisgros grew animated as he neared the lobster tanks and began pulling samples from the water to show his companions the difference between the male and female of the species. "Buy only the female," he said, pointing out the sloping markings on the female's shell and the dark coral visable through the underbelly. This led to a Franco-American dialogue when owner Robert Moore told him American cooks usually ask for the male to avoid the coral.

"But," sputtered the chef, "it is wonderful. It is caviar. Furthermore, the meat of the male is tougher."

He explained a favorite way of cooking lobster to bring out the sea flavor. He places seaweed and a little water in a heavy pot. When the water is steaming, he adds the lobster, covers the pot and cooks it for 5 to 10 minutes, depending on size. He then removes the pot from the flame and leaves it covered for one hour. The lobster, still warm, is then removed, split and served with tarragon butter.

Moore cautioned those who attempt to broil lobster in home ovens."A restaurant stove is very hot," he said. "If you turn your own on to broil and immediately to cook the split lobster, you won't get the same result. You should let the oven warm up at 425 degrees for 15 or 20 minutes first and you shouldn't start with butter on the lobster. It will only burn.Add the butter at the end."

Moore's own favorite method with lobster is to boil for 5 or 6 minutes, then split and usually stuff it. He then places it under the broiler to brown the top.

The English channel lobsters Troisgros buys in France cost him (wholesale price) $10 a pound, he said. The retail price here last week was $4.29, a bargain - in relative terms at least. Troisgros and the chefs that are his friends make much of going to market daily. Told that most restaurant chefs here shop by telephone, he said curtly. "That's idiotic." He also confirmed that he had not found a restaurant equal to the great French restaurants in this country.He blames the structure of the industry rather than lack of skill on the part of chefs here or inferior ingredients.

"It's necessary for the cook to be the owner," he said. "He must be completely in charge, not just a maker of sauces. He should be free to make whatever the market dictates, not forced to use inferior products just because there is a large printed menu. There is too much emphasis in the kitchen on what food costs and not enough on quality."

Roy Andries, DeGroot, among others, has called Troisgros, "the best restaurant in the world." Jean Troisgros is hardly humble, but he did surprise his companions by offering a rival nomination.

"The best restaurant in the world beyond doubt," he announced to his eager listeners, "is Maison des Arabs in Marrakech, Morrocco. A mother and her daughter do the cooking." He paused a moment. "But the mother is dead now. Maybe it has gone down. That was 10 years ago."

There are no reports of decline at Troisgros. When one brother travels the other remains at the stove and usually bother are in the kitchen during each service. According to Jean, there is a rather unusual division of responsibility when both are there. His brother oversees all the cold preparations and selects the wines. Jean is in charge of sauces and hot foods.

These recipes have been translated from "The Original Recipes of Jean and Pierre Troisgros." The book has been sold to an American publisher and will appear here in English, possibly late next year. MISER'S VEAL SCALLOPS WITH MUSTARD SEED (Serves 4) 16 very small veal scallops, each weighing just over an ounce and flattened to 3 inches-by-2 inches. Salt and freshly ground pepper 1/4 cup mustard seed 1 tablespoon Dijon mustard 3 tablespoons peanut oil 3 1/2 tablespoons unsalted butter 1 teaspoon tarragon mustard 1/2 cup chicken bouillon

Season the scallops lightly with salt and pepper and put them on sheets of waxed paper. Spread the mustard seed on a large plate or counter and turn the veal onto the mustard seed. Press lightly to create a crust of seeds. Using a brush, daub the top side with Dijon mustard.

In a heavy bottomed skillet heat the peanut oil and 1 1/2 tablespoons of butter. Just as the grease begins to smoke, add the scallops, mustard-seed side down. Cook 1 minute, the turn and cook 1 minute more. Remove from the pan and keep warm on a platter covered with a plate.

Pour off the grease, add the bouillon and boil down by a third, scraping the bottom of the pan with a wooden spoon to dislodge any brown bits stuck to it.Return the scallops and their rendered juice, cover the pan and keep over a low flames so the liquid does not boil.

Just before serving, arrange the scallops on a plate so they overlap with the grain side up. Add the tarragon mustard and remaining butter, cut in small bits, to the pan and stir until the butter melts and a sauce forms. Spread over the veal. SCALLOPS OF SALMON WITH SORREL (Serves 4) 1 piece (2 pounds) fresh salmon, cut into two fillets 2 tablespoons vermouth 1/4 cup dry white wine 1 cup fish fumet* 2 shallots, chopped 1 3/4 cups creme fraiche 3 ounces (scant) fresh sorrel, stems removed, washed and large leaves torn in 2 or 3 pieces. 3 tablespoons butter 1 tablespoon peanut oil Juice of 1/2 lemon Salt and freshly ground pepper(FOOTNOTE)

* Substitue half clam juice and half water

Remove small bones from salmon fillets with tweezers, then cut each fillet into 4 scallops. Flatten them gently between waxed paper to obtain pieces of equal size.

In a non-aluminum saucepan mix the vermouth, wine, fumet and chopped shallots. Bring to a boil and reduce until the liquid is syrupy and almost a glaze.Add the creme fraiche, stir and let it reduce until it coats a spoon. Add the sorrel and cook for 25 seconds. Remove from the heat and add the butter in small pieces, moving the skillet instead of stirring so as not to break up the sorrel piece. Add lemon juice to taste, salt and pepper. Keep warm.

Heat a large skillet (without oil if it is non-stick), season the salmon with salt and pepper on the least attractive side and place in the pan, seasoned side down. Cook for 25 seconds, turn and cook 15 seconds on the other side.

Pour the sauce into 4 large, hot plates. Wipe any grease from the salmon pieces and place two atop the sauce on each plate. Serve at once.(END FOOT)