One of masterpieces presented by Alfred Girardet, the brilliant young Swiss Chef, during a dinner at his restaurant in the Lausanne suburb of Crispler last winter was a dish of shellfish swimming in a vegetable flavor sauce. Like other souvelle cuisine creations, Girardet's dish was basically simple, relying on the quality of the ingredients and exact cooking to lift it above the ordinary.

Use of a French hand julienne grater or a food processer greatly speeds the vegetable preparation. The final step, scattering of grains of caviar over each portion, is a memorable panace, but also serves a culinary purpose: The salty roe acts as a seasoning agent. What follows is an adaptation worked out in an American kitchen. SHELLFISH WITH CAVIAR

(Serve 6) 1 pint oysters in their liqueur 1/2 cup dry white wine 1/2 cup clam juice 12 large shrimps or langoustines, pleeled 13 sea scallops (if large, buy 9 and cut them in half) 1 large carrot, peeled and shredded 1 medium leek, white part only, shredded 1 large rib celery, shredded 1 teblespoon chopped parsley 1/4 cup Creme fraiche Salt and freshly ground pepper to taste 1 tablespoon butter Black caviar to taste

Strain oyster liqueur into a non-aluminum frying pan. Set oysters aside. Add wine and clam juice to pan and bring liquid to a boil. Cook shrimps at a simmer, turning to barely cook through in about 3 minutes. Lift from broth in a slotted spoon and transfer to a bowl. Season with salt. Keep warm.Cook scallops in broth until just firm and transfer to bowl with shrimps. Season them. Do the same with the oysters.

Add vegetables to broth, turn up heat and cook at a brisk simmer until they are just tender. Stir in Creme fraiche and parsley. Taste broth and adjust seasoning as desired with salt and pepper. Return shellfish, mix ingredients well and allow to heat briefly. Deal out portions into soup plate with the slotted spoon, bring sauce to a boil, stir in butter off the heat and pour over shellfish. Sprinkle about half a teaspoon of caviar over the shellfish in each plate and serve immediately.(FOOTNOTE)

* Creme Fraiche may be purchased at several markets in the area or may be made by mixing 3 tablespoons plain yogurt into 1 cup heavy cream, covering the bowl and leaving it for several hours or overnight in a warm place (such as a turned off gas oven.) (END FOOT)