One afternoon a few weeks ago in Washington, Va., Eunice Sisk leaned over her white picket fence and traded chef Patrick O'Connell a bouquet of peonies and roses for a slice of freshly baked apple tart. Sisk and her husband, Irving, ate their tart that evening. Sitting in rockers on their patio, they breathed in the aroma of rich food wafting out of the Inn at Little Washington's kitchen door. The Sisks have never dined at the inn. "We only eat at midday. Food doesn't agree with us in the evening," Eunice Sisk explained.

The peonies and roses on this occasion worked their way into a table arrangement for the second annual Washington Dames d'Escoffier dinner. But it might have been any meal at this restaurant, for the 36-year- old O'Connell regularly builds his "new" American menu and ambiance around the abundance of local fresh foods and flowers found in this town of 150 people.

"Inn" is a misnomer for the eclectically elegant restaurant with homemade lace curtains and delicately painted ceilings. Until O'Connell and his partner Reinhardt Lynch bought the building five years ago, it had been an old garage with a dance hall upstairs.

The historic inn at Washington, where George Washington danced when he was surveying the town in 1749, is the white clapboard building across the street. Paul and Edna Walker closed the original inn in 1948. Now they live at one end of the building and their daughter, Fran Eldred, runs her Washington's House of Reproductions, a souvenir and secondhand shop, from the other.

Skeptical at first that a fancy restaurant could make a go of it in Washington, Va., but moving into the swing of things after the inn began attracting tourists to the sleepy village, Edna Walker appointed herself chief guardian of the flowering geraniums and petunias in the urns beneath the columned entrance. Fran, the town magistrate, who commands the best view of the back door from the steps of her store, became the inn's self-appointed P.R. lady. "I got some idiot here for his golden anniversary. He's driven out from big Washington with no reservations, and I try to help him get in." Fran baby-sits for the children of adults who want to eat in peace and quiet. She makes it quite clear that the inn is not for families dining out.

The inn's two doors are one of the town's main entertainments. At night the action is at the front door, as guests arrive, often stepping out of limousines. By day it's back-door deliveries. Twice a week Dorothy Kuncewicz drives up from Flint Hill with 200 heads of crisp hydroponic lettuce. Miriam Harris drops off eggs and bright red organically grown strawberries from her Jordan River Farm six miles away. From Harrisonburg comes Esther Mitchell's front- porch applewood-smoked trout.

Back-door bartering is also a way of life at the inn. "The people of Rappahannock County know that we'll buy or trade food for anything which is young, fresh, and picked that day," says O'Connell. "Most people here make one rhubarb pie per season and throw away the rest of their fruit. From their leftovers we make a julienne of rhubarb and leeks with chicken and a rhubarb mousse."

Receiving money for excess garden foods is not fair play in Little Washington. Swapping is. The inn's bartender, Marion Lee, might trade her home- grown rhubarb for a smoked trout. The Sisks prefer homemade ice cream.

Others, like Mattie Ball Fletcher, present a swapping challenge. Of an unspecified age, somewhere above 90, Mattie Ball considers it "too commercial" to sell her delicate candied grapefruit peel, which O'Connell finds superior to Fauchon's. A compromise was reached. Now Mattie Ball sells the candy but she softens each sale by serving her homemade Sally Lunn bread or bought- bread sandwiches filled with fresh parsley and chives from her garden and in the summer fresh mint tea. "Not much secret in this recipe, just much trouble," she laughed, leaning on her homemade triangular walking cane in front of the well that waters her herb garden.

"Opening a restaurant in this forgotten and forlorn area was much like pioneering. No real restaurant had existed since the old-fashioned country cooking served at the Washington House. We had to draw on a labor force which had never eaten in restaurants before," O'Connell said. Today the inn employs 25 people, one-sixth of the population.

That evening's dinner brought to life the town behind the restaurant, each complementing the other in a triumphant counterpoint of local food and flowers against French culinary techniques. The fresh flowers were arranged by Marion the bartender-rhubarb supplier. The dining room stove was filled with the horn of Little Washington's plenty, which was flanked by long strands of rhubarb. And the meal, one dish after another, featured local ingredients: assorted canap,es with applewood-smoked Virginia trout, huge local radishes served with quackers (fried duck skin), 1980 Seyval Blanc aperitif from Middleburg's Meredyth Vineyards, turnips baked in Shenandoah Pride cream, fresh spinach timbales with a minted b,earnaise, hydroponic lettuce with herbs gathered that day, Charlottesville gouda, a mousse of Marion Lee's rhubarb with organic yellow cr,eme anglaise, and, of course, to go with coffee, Mattie Ball's Fletcher's grapefruit slices. Inn at Little Washington, Washington, Va., 703/675- 3800. Open Wednesday through Sunday for dinner only. Dinners from $25 a person. Reservations strongly recommended.

Turnips in Cream Serves 6 to 8 12 medium turnips (about 4 pounds), peeled, sliced paper-thin in circles 1/2 medium onion, sliced paper-thin in circles Salt and freshly ground pepper to taste Freshly grated nutmeg to taste 3 cups heavy cream

Place half the turnips in a greased 8-cup gratin dish. Place half the onions on top. Add salt, freshly ground pepper and nutmeg to taste. Repeat, using up the turnips and onions. Season again to taste. Cover with cream.

Bake 20 minutes in a 375- degree oven. Press the turnips down to make sure all the vegetables are submerged in the cream. Return to oven and continue cooking another 20 minutes or until a golden crust forms on top. Spinach Timbales (Serves 6 to 8) 1 pound fresh spinach 3 tablespoons unsalted butter 2 teaspoons flour 3/4 cup milk 1/2 cup heavy cream 1 teaspoon salt Freshly ground pepper to taste 1/8 teaspoon freshly grated nutmeg 3 large eggs

Pick over the spinach, removing stems and washing carefully. Drop into salted boiling water. Let water return to boil. Drain spinach in colander. Cool with cold water and squeeze dry. Chop spinach finely.

Make a roux with butter and flour. Add the milk, cream, salt, pepper and nutmeg. Bring the mixture to boil and remove from heat. Stir in spinach, cool slightly and beat in the 3 eggs. Fill 8 buttered timbale, dariole or baba molds or even heavy muffin tins and place in a pan of cold water. Bake in a preheated 375-degree oven 25 to 30 minutes or until set. Run a knife around the edge and unmold.

Fruit Mousse 2 pounds fresh rhubarb (11/4 pounds diced frozen or fresh with stems removed) or 1 1/4 pounds

blueberries 1 cup sugar for the rhubarb or 1/2 cup for the blueberries 1 package gelatin 1/3 cup lemon juice 1 cup whipping cream 1/4 cup sugar 1 teaspoon vanilla

Place the diced rhubarb or the blueberries in a heavy noncorrosive pot with the sugar and cook on low heat, stirring occasionally until fruit is soft. Set aside 1/2 cup of this mixture. Pur,ee the remaining fruit through a food mill and cool.

Soften the gelatin in the lemon juice and dissolve over boiling water in a double boiler. Add the gelatin to the fruit pur,ee and stir well.

Whip cream and flavor with remaining 1/4 cup sugar and vanilla. Fold whipped cream into fruit pur,ee alternating with the unstrained fruit. Ladle the mixture into 1 large or a half-dozen small lightly oiled decorative molds. Refrigerate several hours or overnight. Unmold and serve as is or with cr,eme anglaise, fresh mint and a dollop of whipped cream.