English cookbook author Jane Grigson seems to be an expert on just about anything you can eat. Her volume on charcuterie is a reference classic and her fruit and vegetable books, published here by Atheneum, are sybaritic celebrations of orchard and garden.

Currently she is updating a weighty work on fish, so when she was in Washington recently, I whisked her down to take a look at the Chesapeake Bay.

The sun shone, the water shimmered and, looking ahead to summer, we set to planning a picnic based on the best the Eastern Shore could offer. "How about pan bagnat, a sort of salade Nic,oise in a sandwich?" asked Grigson as we sought something portable. THE MENU A PICNIC ON THE EASTERN SHORT FOR 8

Pan Bagnat

Garlic Roast Chicken

Roast Pepper and Bean Salad

Old-fashioned Peach Tarts

Suggested drink: a chilled rose wine or chilled fresh lemonade

Her version, packed in a long French loaf, includes tomato and egg, laced with olives, capers and anchovy. "It must have something crisp, something salty and something moist," remarked Grigson. Basted liberally with olive oil vinaigrette, the sandwich is tightly wrapped and left overnight for its Mediterranean flavors to marinate and mingle.

Fish is tricky in the heat, so for main courses we opted for local chicken, which Grigson suggested cooking with garlic butter spread under the skin so the bird bastes automatically as the butter melts. Brushed with olive oil and cooked at a high temperature, the skin turns crisply golden while the meat remains juicy.

To add color, Grigson opted for bell peppers in a multicolored salad of red, green and yellow. The peppers, roasted to loosen the skin and give a charred taste, are tossed with fresh thyme, oil and lemon.

"Let's see," mused Grigson, "we need some substance. White kidney beans would be good in with the peppers. And for vegetarians, you could add some crumbled goat cheese and forget the chicken."

For dessert I sang the praises of fresh local peaches and she concurred. "How about my favorite old-fashioned tart," said Grigson. "We make it every year for the garlic and basil fair in France at Tours. The inn supplies drink, everyone brings something to eat and this is our contribution."

It certainly must receive a warm welcome. When I tried the tart, I found the cream filling cooked to a buttery golden brown enclosing moist little islands of peach. Like all of Grigson's recipes, it has the simplicity of a master hand. Timetable

The perfect lazy picnic schedule, with all preparations made a day ahead.

Up to 2 days ahead: Roast chickens, let cool, wrap and refrigerate.

Up to 1 day ahead: Make pan bagnat, wrap and refrigerate. Make pepper and bean salad and keep in refrigerator. Bake peach tarts and store in airtight container. Chill wine; make lemonade and chill. Pack picnic basket.

In the morning: Pack food in insulated containers. Pack drinks over ice. PAN BAGNAT (8 servings)

You can experiment with canned sardines or tuna rather than anchovy.

FOR THE VINAIGRETTE DRESSING:

1/4 cup red or white wine vinegar

1 teaspoon dijon mustard

Salt and pepper to taste

3/4 cup olive oil

FOR THE SANDWICH:

A loaf of French bread

Small head romaine lettuce

1 bermuda or sweet red onion, thinly sliced

3 medium tomatoes, cored and sliced

4 hard-cooked eggs, shelled and sliced

1/2 cup pitted ripe olives, coarsely chopped

2-ounce can anchovy fillets

2 tablespoons drained capers

2 tablespoons chopped chives

For the dressing: in a small bowl whisk vinegar with mustard, salt and pepper until mixed. Gradually whisk in olive oil so dressing emulsifies; taste for seasoning.

Cut bread in half lengthwise, scrape out some of the crumb with a spoon and brush generously with dressing. Line bottom crust with lettuce leaves, add layers of onion, tomato and eggs and season lightly. Top eggs with olives, anchovy, capers and chives and spoon over dressing. Note: layers should be moistened but not soaked.

Top with other half of bread and press layers firmly together, wrap loaf tightly in plastic wrap and refrigerate overnight. Carry in the wrap and cut in lengths for serving. GARLIC ROAST CHICKEN (8 servings)

Good hot as well as cold.

1/2 cup (1 stick) butter

4 cloves garlic, crushed

Salt and pepper to taste

2 4-pound roasting chickens

1 to 2 tablespoons olive oil (for brushing)

Cream butter and beat in garlic with plenty of salt and pepper. Insert your hand under skin of chicken and gently detach skin from meat on legs as well as breast, being careful not to tear the skin. Spread meat with garlic butter.

Truss the chickens, brush with olive oil and sprinkle with seasoning. Set chickens in a roasting pan and roast in a 450-degree oven until juice drained from center of birds no longer runs pink, 50 to 60 minutes. Baste chickens often during cooking and lower oven heat to 375 degrees after 15 minutes.

Let chickens cool, then keep in refrigerator up to 2 days. Discard trussing strings and wrap in foil to carry. Cut chickens in pieces in the kitchen, or on the picnic. ROAST PEPPER AND BEAN SALAD (8 servings)

The combination of white beans with green, red and yellow peppers makes a striking salad.

2 green peppers

2 red peppers

2 yellow peppers, or more red or green ones

* FOR THE DRESSING:

2 tablespoons lemon juice

1 teaspoon dijon mustard

Salt and pepper to taste

1/2 cup olive oil

FOR THE BEANS:

3 cups cooked white beans, drained and rinsed

1 to 2 sprigs fresh thyme or oregano

Cut the peppers in half, discarding seeds and core. Broil until skins are well charred and peel easily, 10 to 15 minutes. Note: if not sufficiently charred they will be difficult to peel. Alternatively roast them on a spit. Cover with wet paper towels and let cool.

For the dressing: whisk lemon juice, mustard, salt and pepper until mixed. Gradually whisk in oil so dressing emulsifies. Taste it for seasoning.

Mix beans with peppers and pour over dressing. Strip leaves from thyme or oregano, add to salad and mix well. Taste salad for seasoning. It can be kept 24 hours in the refrigerator. Pack in a plastic container to carry and serve at room temperature. OLD-FASHIONED PEACH TARTS (16 servings)

This recipe comes from "Jane Grigson's Fruit Book," published by Atheneum in 1982.

FOR THE SYRUP:

2 1/2 cups water

1 1/2 cups sugar

FOR THE TARTS:

3 pounds peaches

2 10-inch baked pie or tart shells, 2 inches deep

5 eggs

1 cup sour cream

1 cup whipping cream

1/4 cup sugar or to taste

1/2 cup (1 stick) butter

For the syrup: heat water and sugar until dissolved, then boil 3 minutes. Halve half the peaches, discarding pits, and add to syrup. Set a plate on top so peaches are completely immersed and poach until tender and skins start to wrinkle, 10 to 15 minutes. Drain peaches and poach remaining ones in the same way.

Peel peaches, cut them in quarters and tightly pack in circles in the pie shells. Whisk eggs to mix, stir in sour and whipping creams with sugar to taste. Melt butter, stir into mixture and pour gently over peaches.

Bake tarts in a 425-degree oven until filling is lightly brown, about 20 minutes. Lower heat to 350 degrees and continue baking until filling is set, 30 to 35 minutes longer. Take from oven and let cool.

Meanwhile, boil poaching syrup until it reduces to a thick syrupy glaze. While tarts are still warm, brush them generously with glaze. If using tart pans, transport the tarts in the pan and unmold when served. Tarts are best eaten the day of baking, but they can be stored in an airtight container for 24 hours.