CHEAPER than going to a restaurant, easier than giving a party and as much fun as looking in somebody else's refrigerator. A potluck supper is the cook's ideal night out.

This great democratic institution spreads the workload and gives everyone a taste of something new. It allows a cook to show off but in a modest way. To cooks looking for new ideas it is more satisfying than reading a food magazine, because the recipes are there to taste. For cooks who thrive on thrift it is a subtle and generous way to clean out the refrigerator.

No less rewarding for the eaters than the cooks, a potluck affords a chance to sample something new without committing oneself to a whole portion, to compare a half-dozen styles of the same dish, to slyly indulge in a favorite course, say seven kinds of macaroni, or only tomatoes.

But there is a serious side to the potluck; it offers rich material for research on the true eating habits of the American people. The potluck is today's cookbooks come alive, today's casseroles uncovered. Market researchers find it easy enough to document what Americans are buying, but to find out what they are cooking--for that you have to get invited to a potluck.

Thus a research project was undertaken at the annual potluck supper for the parents of Lowell School in Northwest Washington. The school was willing to cooperate by having the cooks bring a written recipe with each dish. And the parents agreed to be the subject of this important study.

There was no pasta primavera.

That startling finding alone will pinpoint this as a landmark study in the annals of American taste.

It was clear that some things never change. The appetizer table held three creamy dips; it always has and always will, though this time the Doritos were flanked by whole-grain crackers of rice, rye and wheat. Ritz and saltines are but a memory.

Hummos is hanging in there. Pa te's were reduced to one meat and one vegetable, three layers alternating spinach, onion and tomato. "It seemed like a good hot-weather thing," cook Ellen Rashbaum started to explain about her vegetable pa te'; then she got to the crucial consideration, "it's dietetic." Instant hits were a salsa with pickled red peppers, celery, green peppers and olives and home-smoked trout. The cheese ball has been replaced by the cheese log, and cheddar by goat cheese. Kathleen Boswell had picked up the idea from a magazine for rolling logs of goat cheese in walnuts, chives, cracked pepper or thyme and arranging them on a tray of ivy leaves from her garden.

Parsley has not actually disappeared, but it is being upstaged by flowers and leaves as decoration for platters.

While the food manufacturers scream Mexican, the potluck table persists with Sichuan. Sichuan Peppercorn Chicken, Sichuan Chicken Salad, Chinese Chicken Wings. In any case, a potluck table is bound to have something hot. Just as it will always have lasagna (down to two at Lowell School) and inevitably quiche (again a mere two, though artichoke and mushroom rather than the everyday cheese), a curry, a potato salad, some kind of macaroni, several green salads and at least one with pineapple or mandarin oranges.

And always the mainstay of a potluck will be chicken, at least as long as chicken is cheap. Miriam Freilicher did a little "California style" experimenting with hers, winding up with raisins, nuts and chili powder and a title of Chicken Monterey. Mark and Betsy Stumpf seasoned their chicken with rosemary; Carole Flores added white wine along with the rosemary in her Chicken Scarpariella. There were chicken crepes and chicken salad with tarragon and broccoli.

What wasn't chicken was hamburger; as Christopher Klose explained of his Convent Casserole, it is a matter of "loaves and fishes--I didn't know how many people I had to feed." Ellen Herscher's Cypriot musaka, which she learned while working on an archeological excavation, was time-consuming but had advantages; it could be prepared in stages over several days, and it could be served hot or cold.

Sometimes there are elegant bonuses such as David and Betsy Hawkins' Fettuccine Natasha, chosen because they had a pound of smoked salmon in the freezer that they wanted to use up.

The bulk of any potluck is bulky dishes, the starches. Potato salad will, one hopes, never die, though macaroni salad is history. Pasta salads thrive but at Lowell School this year there were three taboolis (probably a short-lived trend, since there is only so much you can do to vary cracked wheat, mint, parsley and lemon juice). Rice salad remains slow and steady, and for good reason. It is cheap and easy to make, can be infinitely varied and made ahead. It can be beautified with the tinting of golden or rosy spices, sweetened with raisins or apricots, flavored with broths as it cooks, molded into tidy shapes and garnished with nearly anything.

Potluck vegetables are better than ever. Lowell School's asparagus was fresh and flecked with sesame seeds. Cold peas, corn and celery were tossed with olives and a vinaigrette for a cooling salad. And the ubiquitous three-bean salad was made by cookbook author Betsy Mirel, so it was no out-of-a-jar dullard. She used freshly cooked beans--"pink beans because they don't mush up like kidney beans," she said--plus chick peas and green beans.

Traditionalists come home to the dessert table. Certainly no potluck in the history of the United States has gotten away without brownies, though Lowell School's ventured into chocolate mint. There were three apple pies and the required array of strawberry desserts--tarts and cheesecakes.

As always, there was a cheesecake that its maker said was the best in the world: Beth Sarfatti "took the best sour cream cheesecake and took the best heavy cream cheesecake and took the best lemon cheesecake" and combined the most caloric parts for a cake that has "gone the limit," then topped it with glazed strawberries and whipped cream. The most adventurous dessert was cre me brule'e; and sure enough, Estelle Rogers brought it because "it's a little different from brownies."

Certainly no reliable conclusions can be drawn from this research until another decade of potlucks has been devoured. I mean studied. In the meantime, here are some suggestions for potluck cooks and some recipes from the Lowell School project:

* Choose dishes that can be served at room temperature, for oven space is usually insufficient and reheating often means overcooking.

* Bring hot dishes wrapped in many layers of newspaper, a good insulator that can keep large casseroles warm for hours.

* Choose dishes that can be made ahead. Not only do they preclude last-minute rushing, they are also those dishes that withstand hanging around on a potluck table.

* Cut portions small; guests want to sample a wide variety rather than have a whole chicken breast filling up their plate.

* Label your food. Some people have allergies and aversions; others might pass unfamiliar-looking foods they would love.

* Decorate foods attractively; they will be viewed for far longer than they will be tasted.

* Don't forget to bring utensils for serving the food, and put the food in a pretty container. Said Betsy Mirel, after three children in three schools, "I learned long ago that nothing ever happens to a pretty dish in a potluck."

* Look for your own food on the buffet; many a potluck dish has languished forgotten in the communal kitchen. ROSALIE MANDELBAUM'S TABOOLI (8 to 10 servings) 1 1/2 cups No. 2 bulghur or cracked wheat 5 scallions 1 bunch parsley 1 tablespoon vinegar 2 tomatoes (or more), peeled, cored, seeded, chopped Salt to taste Juice of 2 lemons 10 fresh mint leaves 1/2 cup olive oil or to taste 12 tender romaine or boston lettuce leaves

Place bulghur in mixing bowl. Add 2 quarts water. Let stand 2 hours or untill softened. Drain in colander lined with cheesecloth; squeeze thoroughly. Place in mixing bowl. Trim scallions, rinse, dry and chop fine. Add to bulghur. Wash parsley in vinegar mixed with cold water, drain and dry on paper towels. Add to bulghur. Add tomato, salt, lemon juice and toss well. Refrigerate until ready to serve. Tear mint leaves with hands. Add oil and toss. To serve, arrange on bed of lettuce leaves. Adapted from "The New York Times International Cookbook" CAROLE FLORES' CHICKEN SCARPARIELLA (Chicken Shoemaker Style) (6 servings) 1 1/2 cups olive oil 3 small broiler chickens, cut into serving pieces Salt, freshly ground pepper 1 teaspoon chopped garlic 1/2 tablespoon chopped parsley 1 1/2 teaspoons rosemary 2/3 cup dry white wine

Heat oil in 1 large or 2 small skillets until very hot. Salt and pepper chicken and fry over high heat until a golden brown. This should take no more than 10 minutes. Add garlic, cook until golden, being careful not to let it burn. Add parsley and rosemary. Remove pan from heat and mix in wine. Return to low heat and cook until wine evaporates (about 10 minutes). Serve with pan juices poured over chicken. SUSAN O'SULLIVAN'S SICHUAN PEPPERCORN CHICKEN (4 to 6 servings) 2 whole chicken breasts 4 slices fresh ginger 4 scallions, including green tops 1 head romaine lettuce 1 teaspoon sichuan peppercorns, crushed 1/4 cup vegetable oil 1/4 teaspoon red pepper flakes 1 tablespoon dark corn syrup 1 tablespoon hoisin sauce 1 tablespoon dark soy sauce 2 cloves garlic, finely minced

Put chicken breasts in a pot with enough water to cover; add 1 slice of ginger and 1 scallion. Bring to a boil, cover and turn flame to medium. Cook 15 minutes, turn off heat and let stand in water 20 minutes more. Cool chicken, bone, skin and tear into shreds.

Chop remaining scallions and mince remaining ginger. Shred lettuce.

Combine crushed peppercorns, vegetable oil, chopped scallions, ginger and red pepper flakes in small saucepan and boil 1 minute. Combine corn syrup, hoisin sauce, soy sauce and garlic in bowl. Add to hot mixture and mix. Combine chicken shreds and lettuce, add sauce and toss. FANNY'S MUSAKA (Ellen Herscher's Cypriot Musaka) (8 to 10 servings) 3 pounds zucchini 3 pounds eggplant 1 1/2 pounds large firm tomatoes 1/2 cup vegetable oil 1 large onion, chopped (about 1 cup) 3 pounds ground beef 1 large bunch parsley, chopped 2 6-ounce cans tomato paste Salt and pepper to taste 1/2 teaspoon cinnamon For the topping: 6 tablespoons butter 6 tablespoons flour 3 cups milk Salt, pepper and cinnamon to taste 4 egg yolks 1/4 cup grated parmesan

Slice unpeeled eggplant and zucchini, crosswise, into about 3/8-inch-thick slices; slice tomatoes in 3/4-inch-thick slices. Brush vegetable slices lightly with oil, broil until brown on both sides and drain off any fat that accumulates. In large frying pan, cook chopped onion in 1 tablespoon oil, until soft. Add ground beef and brown; drain off excess fat. Add parsley to meat mixture, cook about 3 min. Stir in tomato paste, salt and pepper to taste and cinnamon.

Make layers in 10-by-14-by-2-inch baking dish as follows, lightly salting each layer: half of zucchini, half of eggplant, meat mixture, tomatoes, remaining zucchini, remaining eggplant.

Make the topping by melting 6 tablespoons butter in saucepan. Add flour and stir until blended and bubbling. Add milk and cook over medium heat until thickened and smooth. Add salt, pepper and a dash of cinnamon to taste. Combine small amount of hot sauce with egg yolks; return to saucepan and cook over low heat until thickened. Spread topping over layered meat and vegetables. Sprinkle parmesan evenly on top. Bake at 375 degrees until bubbling and brown on top, about 45 minutes.