WHAT LOOKS like an apple, smells like perfume and has a tart flavor? A quince. Once widely popular in this country because of its high pectin content and usefulness in setting jelly, the strongly aromatic quince is now a relatively obscure fruit.

Yet there is still a demand for quince. People of Middle Eastern cultures consider it a delicacy. It has even had mystical qualities of fertility attached to it. According to Plutarch, Solon (Athenian statesman, c. 649-559 B.C.) enacted a law that the quince should be the invariable feast of each newly-wedded couple before they retired to their nuptial couch.

The quince is best known for its preserves. In fact, our word for marmalade comes from the Portuguese word marmelo, meaning quince. This tart fruit can be used to make jelly, compote, wine, liqueur and confections like quince paste. Stuffing a Thanksgiving goose with quince, nuts and rice adds an exotic touch to a traditional American holiday. And the addition of a few quinces can transform an excellent apple pie, tart or custard into an unusual, superb dish.

When ripe, a quince has a rich golden yellow color, and is covered with a fuzzy down which must be washed off before use. It is a very tart fruit, considered by some to be inedible fresh from the tree. Yet in Greece, "The quince is mostly eaten raw," says Leonidas Panagopoulos, manager of Alexandria's Greek restaurant Taverna Cretekou. "But it has to be ripe." Panagopoulos remembers eating quinces as a child in Greece. "My mother used to make quince compote. I had it for breakfast every morning. I miss it."

There is a saying in Greece, adds Panagopoulos, that "if you have a quince tree in your yard and it has many fruits, it means you have fertility and will have many children."

The true quince was cultivated early by the Greeks. Its botanical name, Cydonia vulgaris, comes from Cydon, a city on the island of Crete. nIt must be distinguished from the Japanese Quince (Chaenomeles speciosa), a popular ornamental shrub which blooms early in the spring and produces a hard, sour fruit in the fall. These yellow-green quinces are totally inedible raw, but make an exquisite jelly.

Use of the quince in the 19th century was not limited solely to cooking and eating. "Medicinally, the quince is cooling and strengthening," wrote William Meech in his 1896 book "Quince Culture." "The juice is good against nausea." In 1831, Henry Phillips reported the cure of a severe case of asthma at Harsham, in Sussex, England, with the use of quince wine.

Over the centuries, the quince spread to Italy and England, and was later brought to New England by the Pilgrims. It is now grown in California, Pennsylvania and New York.

"The people who buy quinces, mostly of Middle Eastern origins, usually pay close attention to the cost of food," says Nade Gordon, general manager of the Hampshire Open Air Market (one of the few places that sells quinces). "But with quinces, they don't care. They don't even ask. It is something they want because it is part of their culture -- and they find it hard to get." They cost 50 to 80 cents apiece.

Dr. Miklos Faust, head of the Fruit Research Laboratory, U.S. Department of Agriculture, remembers the quinces of his youthful Hungary. He attended a school much like one of our boarding schools. "I used to put quinces under the mattress of my bed at school," says Faust, "between the mattress and box springs.They would stay there until they got soft, usually some time in January or February. Then we would eat them. Quinces are very, very good and have a unique flavor."

Locally, quinces may be found at:

Chevy Chase Supermarket, 8531 Connecticut Ave., Chevy Chase, Md. 656-5133.

Co-Op Consumer's Supermarket, 3715 University Blvd., Kensington, Md. 942-9611.

Hampshire Open Air Market, 6501 New Hampshire Ave., Hyattsville, Md. 270-4900.

Magruders Grocery: Chevy Chase, Washington, D.C. 244-7800. Rockville, Md. 881-1181.

Sol Stalins, Inc., 1325 5th St., N.E., Washington, D.C. 547-7900 (Sells by the case only.)

Thomas Market, 2650 University Blvd., Wheaton, Md. 942-0839.

Bethesda Avenue Co-Op, 4949 Bethesda Avenue, Bethesda, Md. 986-0796.

Straight from the Crate, Penn Daw Shopping Center, Alexandria, Va. 768-7283.

Coleman's Roadside Market, 6673 Little River Turnpike, Annandale, Va. 750-9683.

Jim's Country Market, 6501 Franconia Road, Springfield, Va. 971-9808.

Reston Farm Market, 10800 Baron Cameron Avenue, Reston, Va. 759-3127.

Magruder's Grocery, 180 Maple Avenue, West, Vienna, Va. 938-4700. QUINCE JELLY (Makes 3 cups) 3 pounds quinces, about 9 or 10 Sugar 2 tablespoons lemon juice Rose geranium leaves, optional

Wash, quarter, core and slice the fruit. Do not peel. (But if you intend to save the pulp to make the following recipe for quince paste, peel the fruit and place the peelings in a muslin or cheesecloth bag. Cook along with the fruit, then remove.) Cover fruit with cold water in an enamel or other non-aluminum saucepan. Bring to a boil and simmer until soft, about 20 to 25 minutes. Mash down the fruit and boil for 5 more minutes.

Using several layers of cheesecloth or a jelly bag, drain the juice into a large bowl for about 10 to 15 minutes. Measure the juice, then return to the saucepan (rinsed clean) and add the lemon juice.Bring to a boil, then add 3/4 cup sugar for every cup of juice measured. (the amount of juice will vary depending on the amount of water added earlier.) Boil rapidly until jelly is done. The jelly turns bright red while it is cooking. To test for doneness, dip wooden spoon in jelly, hold flat for a few seconds, then tilt the spoon. The last drops of jelly will drip together to form a "sheet" when the jelly is done. More accurate -- use a candy thermometer. Jelly is finished when it registers 220 degrees to 222 degrees F. Skim off foam, pour into hot, sterile jelly glasses and top with thin layer of melted parrafin. Do not disturb until cool.

If desired, place a washed leaf of rose geranium in the bottom of each jelly glass. Adds a delicate flavor. QUINCE STUFFING (Makes 4 1/2 cups) 3 cups cored, peeled and chopped quince 1 medium onion, chopped 2 teaspoons sweet unsalted butter 1 stick celery, finely chopped 1/4 cup honey 1/2 teaspoon allspice 1/2 cup coarsely chopped walnuts 4 cups steamed brown rice, cooled

Saute onions in butter until transparent. Add quince, celery, honey and allspice, cover and simmer 20-30 minutes, until quince is tender.Cool slightly, then toss well with the rice and walnuts, and use to stuff a goose. The tartness of the quine blends well with the flavor of a goose or duck. QUINCE COMPOTE (Makes 1 quart) 6 ripe quinces 1 cup sugar 3 allspice berries 1-inch piece of stick cinnamon 1/4 cup brandy

Wash, peel, core and slice the quinces. Dissolve sugar in water over low heat, using an enamel saucepan. Add quinces and spices and bring to a boil. Cook over low heat for about 20 minutes, or until fruit is tender. Turn off heat, remove spices and add brandy. Let sit for 20 minutes to allow flavors to blend, then pour into quart jar and refrigerate until use. Delicious with bread in the morning, or spooned over ice cream. Can be eaten as a bowl of fruit topped with whipped cream. QUINCE-APPLE CUSTARD (6 servings) 6 tart apples 3 to 4 quinces 1/2 cup sugar 2 tablespoons lemon juice 1/2 teaspoon cinnamon 1/3 cup melted butter 6 eggs 1 egg white 1/4 cup rum Caramelized 2-quart round baking dish (souffle dish works well)

Preheat oven to 350 degrees. Peel, core and thinly slice the fruit. Combine with sugar, lemon juice, cinnamon and melted butter. Toss together well and spread out into a large, shallow roasting pan. Bake for 25 to 30 minutes, or until fruit is slightly tender.

In a separate bowl, combine eggs, egg white and rum and beat until frothy. Fold in the fruit and turn into caramelized dish (see note below). Set in a pan of hot water and bake in lower third of preheated oven for 1 1/2 hours or until knife inserted in center comes out clean. Can be served warm or cold. To serve warm, set dish in bowl of cool water for 10 minutes, then unmold.

(Note: To caramelize dish, combine 1 cup sugar with 5 tablespoons water in a small, heavy saucepan. Bring to a boil, swirling constantly. Boil rapidly 3 to 5 minutes after syrup becomes clear, or until sugar has turned a light brown color. Pour immediately into baking dish and rotate quickly to cover bottom and sides.) QUINCE-APPLE PIE (Makes 1 9-inch pie) Pastry for double crust pie 6 apples 2 quinces 1 tablespoon flour 2 to 3 tablespoons sugar 1 teaspoon vanilla 1/2 teaspoon cinnamon 1/4 teaspoon nutmeg Butter, optional

Make pastry (see below) and chill. Peel, core and slice the fruit. Toss with remaining ingredients. Roll out half the pie crust and line pie pan with it. Fill with fruit, then top with remaining crust. Bake in 350 degree oven for 45 minutes. Optional: Before putting on top crust, dot filling with dabs of butter. Pie Crust 2 cups flour 2/3 cup shortening or 3/4 cup butter 1/2 cup cold water

Sift the flour, measure and sift again. Using a pastry cutter or two knives, cut the shortening into the flour until it forms tiny particles about the size of peas or rice grains. Adding one tablespoon of the cold water at a time, press the flour mixture together until it forms a ball. Chill. Rool out onto lightly floured cutting board. NOTE: Pastry rolls more easily when made with shortening, but many prefer the taste of butter.