"Americans have revolutionized the sandwich," observed Claudia Roden as she lifted up a hot pastrami on rye one recent afternoon in New York. An Egyptian-born food writer who now lives in London, Roden has given the subject of sandwiches considerable thought over the past few years.

"The sandwich obviously suits your hurried life style, but you have actually turned sandwich-making into a fine art," she continued, extolling the virtues of the Reuben and club sandwich and waxing eloquent about the imaginative range of filling that has crept between two slices of bread.

"I recently tasted my first meatball hero," Roden added with evident satisfaction.

"The success of the American sandwich lies in the generosity and quality of the filling, and the variety of combinations of filling and bread," she continued. "In England, our sandwiches tend to be quite the opposite. On the one hand, tea sandwiches are thin and dainty. On the other hand, a typical purchased sandwich was fairly accurately described by a British cookery writer at the turn of the century as two disconsolate pieces of mustard-patched bread hiding the slice of tough beef which you are struggling to conceal from your neighbor."

Because of her Middle Eastern heritage and her travels around the world, Roden is quite eclectic in her approach to sandwiches. While she enjoys danish open-faced sandwiches and has added the meatball hero to her repertoire, more often than not, when back on home turf in the Golders Green section of London, Roden enjoys packing a variety of ingredients into pita bread. She finds pita a good pouch for such diverse fillings as mashed potato seasoned with Indian spices or pizza-makings such as mozzarella, tomatoes, olives and anchovies.

"A friend of mine gives an annual picnic for 50 people and always serves an array of salads, beans, cheeses and fish with a towering stack of pita so that people can mix their own fillings," said Roden.

"Pita is also the ideal picnic bread when you want to wrap a sandwich in tin foil and heat it in the fire because leaks are kept to a minimum," added Roden, who researched such things for her book "Everything Tastes Better Outdoors" (Knopf, $19.95).

Here is a selection of Roden's favorite sandwich recipes, adapted from that book. They are ideal for summer picnics or light summer meals. PAN BAGNAT (6 servings)

This recipe is from the Provencal coast of the Mediterranean and is best prepared at least 2 hours in advance, but preferably the day before. The sandwich is usually made in a long french loaf, but is equally good in a round flat peasant-style loaf or in small individual hard rolls.

2 baguettes or 1 large round loaf or 6 hard rolls

2/3 cup olive oil

4 tablespoons wine vinegar

Salt and freshly ground pepper to taste

1 clove garlic, crushed (optional)

1 pound ripe tomatoes

1 large Spanish onion, peeled

2 sweet green peppers

1/2 cup pitted black olives, preferably nicoise

2-ounce can anchovy fillets

Cut the loaves or rolls in half horizontally. In a small jar, shake together a vinaigrette of olive oil, vinegar, salt, pepper and optional garlic. Generously sprinkle both insides of each loaf with the vinaigrette.

Cut the tomatoes, onion and peppers into thin slices, discarding the seeds in the latter. Set a layer of each on the oiled bread. Distribute the olives and anchovy fillets on top and cover with the top halves of the bread. Press the sandwich (or rolls) together and wrap tightly in aluminum foil. Leave in a cool place with a weight on top long enough for the juices and oils to be well absorbed.

To serve, cut into thick slices, or if using a round loaf, cut into wedges like a cake. ARAIS PITA BREAD STUFFED WITH MEAT (6 servings)

If you are taking this sandwich on a picnic, make the filling in advance and keep it warm in an insulated container. Assemble the sandwiches just before eating. 6 large pita breads, warm if possible

1 large onion, peeled and finely chopped

2 tablespoons oil

1 1/4 pounds lean ground veal, beef or lamb

1 small hot green chili pepper, finely chopped

Juice of 1/2 lemon

1/2 teaspoon allspice

1 teaspoon cinnamon

Pinch cayenne

1/2 cup finely minced parsley

Salt and freshly ground pepper to taste

Cut each pita and open carefully without breaking. Set aside.

To make the filling, fry the onion in the oil until golden. Add the meat and fry, stirring, until it turns brown. Add the chili pepper, lemon juice, spices, parsley and salt and pepper to taste and cook an additional 2 to 3 minutes. Adjust seasonings.

When ready to serve, divide the filling and stuff the pitas. CLUB SANDWICH (1 serving)

Most sandwich mavens agree that this is the greatest sandwich of all. Although many restaurants have taken to serving it as a triple-decker, connoisseurs usually prefer just two slices of bread. For best results, use just-made toast lightly smeared with sweet butter.

2 slices buttered toast

Mayonnaise for spreading

Crisp lettuce leaves

3 to 4 slices cooked chicken breast

3 to 4 thin slices tomato

3 slices crisply fried bacon

Green olives and pickle spears for garnish

On each slice of toast, spead a thin layer of mayonnaise and then on one slice layer the lettuce, chicken, tomato and bacon, dabbing a bit of mayonnaise here and there between the layers. Set the top slice in place and cut into 4 on the diagonal.

Hold the sandwich together with toothpicks, if desired. Serve on a plate with olives and pickle spears. MEATBALL HERO (4 to 6 servings)

1 1/4 pounds ground beef

1/2 cup dried bread crumbs

1 clove garlic, finely minced

2 tablespoon finely chopped parsley

1 tablespoon finely chopped fresh basil (or 1 teaspoon dried)

1 lightly beaten egg

Salt and freshly ground pepper to taste

2 tablespoons light vegetable oil

1 onion, peeled and finely chopped

3/4 cup tomato paste

2 1/2 cups peeled, coarsely chopped tomatoes

2 12-inch loaves french bread

1/2 cup grated parmesan

Combine the beef, bread crumbs, garlic, herbs, egg, salt and pepper. Work well with your hands and roll into balls about 1 1/2 inches in diameter. Heat the oil in a saucepan, add the onion and fry, stirring, for about 2 minutes. Add the meatballs and brown them all over, then stir in the tomato paste and the tomatoes. Season with salt and pepper to taste and cook over low heat, covered, for about 30 minutes.

Split the bread lengthwise. Cut the meatballs in half and arrange them on the bread. Top with the tomato sauce and then the parmesan. Press the top half of the loaf into place and cut each loaf into 2 or 3 sections. Serve immediately. English Tea Sandwiches for Picnics

Since English tea sandwiches are meant to be dainty affairs, Roden suggests using thinly sliced white or whole-wheat bread, trimmed of crust or not, as desired. Spread sweet butter on each slice of bread before using one or more of the following fillings, and cut each sandwich into four diagonally, once it is made. The recipes below provide a thin filling for each sandwich; if you prefer thicker fillings, plan on making fewer sandwiches than the recipes suggest.

For a tea-party picnic, prepare a variety of sandwiches and bring along some iced tea with some lemon, lime or orange slices for garnish.

Cucumber: Peel a large cucumber and slice it very thin. Set the slices on a plate. Sprinkle with salt, and set aside for an hour. Drain off any liquid that accumulates, and pat the slices dry on paper towels. Divide the cucumber slices among 6 pieces of buttered bread and sprinkle with a squeeze of lemon and some freshly ground pepper. Cover with an additional slice of buttered bread, slice, and serve.

Sardine: Drain and mash the contents of a 43/8-ounce tin of boneless sardines. Blend in 2 tablespoons cottage cheese to create a nice spreading consistency. Add 2 tablespoons lemon juice and 2 tablespoons finely minced onion, if desired. Season with salt and pepper to taste. Spread the mixture on 3 slices of buttered bread. Set a few sprigs of watercress on top. Cover with an additional slice of buttered bread, slice and serve.

Mushroom: For each sandwich, thinly slice 1 large or 2 medium raw mushrooms and arrange on a piece of buttered brown bread. Season with salt, pepper and a sprinkling of lemon juice. Cover with an additional slice of buttered bread, slice, and serve.

Cheese and Watercress: Blend together 1/2 cup tightly packed, grated sharp cheddar cheese with 2 tablespoons softened butter and 2 tablespoons sour cream. Stir in 1/3 cup finely chopped watercress. Spread the mixture on 4 slices of bread. Cover with an additional slice of bread, slice and serve.