Olives were Plato's favorite food, legend says, and millennia later there are still many cultures all over the world to which a meal, to say nothing of their entire cuisine, would be considered incomplete without the olive.

What would the Mediterranean cuisines be without olives? Missing would be the black olive, anchovy and caper dip of Provence (tapenade) and pot roast provenc,ale, French olive-topped pizza (pissaladie re) and the salade nic,oise of southern France, Italian pasta with olive and tomato sauce (puttanesca) and antipastos, Greek salads with feta cheese and large purple olives.

Middle Eastern cuisine, too, boasts many dishes characterized by the olive flavor: lamb tajine, moroccan chicken, pigeon with olives and lemons.

Olives flavor Chilean empanadas, Mexican picadillo and Cantonese-steamed dishes (in the form of lom gok, a pungent dried black olive). The Chinese also enjoy snacking on sweetened preserved olives with a taste that resembles preserved kumquats.

Americans, on the other hand, are slouches when it comes to olive consumption. While others dote on the delicious berry of this ancient gray-leafed tree, in the United States olives are culinary stepchildren. It is a shame. What other food packs more flavor punch for its size? If olives are an acquired taste, as many people claim, more of us should venture beyond nibbling on the olives in our martinis.

For this baleful situation the California Olive Association and the Cooperative Extension Service of the University of California blame inadequate knowledge of olives, their price, fluctuating supplies and the impression most consumers have that olives are a specialty food. And, many people mistakenly believe that olives are fattening.

They do not realize that a large pickled green olive contains approximately seven calories or that the calorie count of ripe olives is between five and seven. Even the largest olive has no more than 12 calories. According to the California Olive Association, olives are a nutritional bundle of potassium, phosphorus, calcium, iron, copper and beta carotene. Ripe olives include 79 percent moisture, 17 percent easily digestible cholesterol-free oil, 1 percent protein and 1 percent crude fiber.

Independent of its nutritional value, it is hard to imagine cooking without the olive and its oil. Potato, tomato and pasta salads, rabbit stews, braised duck dishes and composed butters for melting over steaks or fish often get an olive flavor boost. Olives are a versatile garnish for appetizer plates. And more and more they are playing a starring role on the appetizer circuit, says Penelope Pate-Green of Sutton Place Gourmet. Like many specialty shops, Sutton Place stocks a variety of loose, canned and jarred olives as well as olive pastes for canape's.

The Roman scholar Pliny wrote, "Except the vine, there is no plant which bears a fruit of as great importance as the olive." The history of this venerated evergreen tree with its hard-stoned berries proves his point.

Olive trees were grown in Egypt as long ago as the 17th century B.C., and the pharoahs' tombs have yielded samples of cured olives. Olives are prominently mentioned in the Bible. The ancient Greeks named the city of Athens in honor of the goddess Athena because she gave humanity the gift of the olive tree. Along with bread, olives (which incidentally were considered aphrodisiacs) sustained many ancient Roman warriors and sailors on long jouneys, and archaeologists have unearthed perfectly preserved examples in the volcanic ashes of Pompeii.

The Phoenicians planted the first olive groves of Spain, and it was the Spanish who carried olives to the New World in the 1560s, where they were cultivated in Peru, Chile and Brazil, as they still are today. By the beginning of the 18th century, Franciscan friars brought olives to Mexico, and by the late 1800s California had a small olive industry.

In each country, the olives changed, as grapes do, with the soil and weather conditions until today there are uncountable horticultural varieties. Olive trees do best planted in arid, dry soil where they thrive if they have dry, hot summers and frost-free winters just cold enough to set the fruit.

The choices are so many that confusion usually reigns among consumers purchasing olives. While barrel after barrel of olives in their "mother brine" are displayed in the open-air markets of the primary growing countries (Spain, Italy, Greece, France, Portugal, Morocco, Turkey, Israel, Argentina and Brazil), not all varieties are exported, so only a relative handful are known and available in the Washington area. Still, choosing is confusing because the hundreds of varieties of the edible olive, Olea europaea, differ in their size, shape, color, flavor and oil content.

Olives may be colossal or tiny, round or oval, blue-green, dark green, dark red, purple-black, black-brown, even straw yellow and firm or soft, wrinkled or smooth.

In the grocery store they are sold in jars, cans or loose and may be classified by the method used to cure them, or by the variety of tree from which they derive or by the town, region or country of origin. Specialty shops sometimes further cloud the issue by creating their own marinades and herb flavorings with their own names.

Annual worldwide production is more than 7 million tons of olives. Spain is the largest producer, more than 2 million tons from more than 210 million trees, primarily of the variety named Manzanillo (what in the U.S. is commonly called the Spanish olive). At least 160,000 tons of this variably sized variety are picked green, lye-cured and packed in a salt brine and often stuffed with pimientos, almonds, pear onions, capers or anchovies.

Greece and Italy follow Spain as the largest producers. Greece is best known for its calamatas (also spelled kalamata), a medium-to-large, almond-shaped, purplish-black or green olive cured in brine and packed in vinegar. There are also salty, shriveled brine-cured black olives called Greek olives. Italy is known for its wrinkled black gaeta olives, first dry-cured and then rubbed with oil.

Several types of French olives are available here, too. Picholines are the best known, a smooth, green, brine-cured olive. Nic,oise olives are small, brownish-black and brine-cured. From France, too, come nyons, rougeons, courcourelles and redoutants. What are known as Moroccan olives, dry-cured, wrinkled black and a little bitter tasting, do come from Morocco, but that country also exports a smooth, black, brine-cured olive. And the purple-hued, brine-cured alfonso olive packed in vinegar and oil is Brazil's most famous variety.

In the United States, California is the principal olive growing area, with approximately 4 1/2 million trees and an average of 55,000 tons of olives, almost all of which are sold for eating rather than oil. The state is best known for the so-called black ripe olive. Missions are the smallest type and sevillanos the largest, while manzanillos, the most popular, are in between with a high flesh-to-pit ratio.

California ripe olives are lye-cured, relatively mild and tasteless when compared with the imported ones. The reason is they are picked green (not naturally ripe and dark) and processed with chemicals that turn them black and shiny. A small number are processed into "ripe" green olives while some are processed and stuffed to become "Spanish-style" green olives. Only a very small percentage of the California olive crop is made into old-world-style olives by a few small companies that produce an artisan-made product.

Craig Makela of the Santa Barbara Olive Company, one of the most successful of these local companies, has been putting up olives since childhood and recently gave up wine making for the olive business. In little more than a year he and his wife Cynthia have developed 16 different styles of olives that are making a strong impact in the specialty food field. Theirs are organically grown, hand-picked and distinguished from canned olives by a lack of preservatives and by being cold packed because Makela believe heat canning cooks the olives and changes the taste.

The flavors of these Santa Barbara olives include red wine, garlic, country herb, black pepper, red pepper and bay leaves, Mexican spices and hickory smoked. The Sevillanos are stuffed with pimentos and marinated in vermouth for the ultimate martini or stuffed with hot serrano peppers and marinated in jalapen o pepper brine. Hot spicy and mild oil-cured olives are new. Greek-style black olives are cured in salt, sun-dried and rolled in oil, black pepper and oregano, and the California black olives are "honest" tree-ripened and naturally dark, unlike the better known artificially colored California black olives.

Nieman Marcus carries the Santa Barbara Olives. Or, a gift pack of four 10-ounce jars of spiced olives and a six-ounce bottle of the Makelas' own cold-pressed extra virgin olive oil can be ordered for $19.95 by calling (805) 965-6358 or writing to P.O. Box 3825, Santa Barbara, Calif. 93105.

The delicious taste of the olives from his home region and the attractive wooden box's stylized picture of a fruit-laden olive branch, long a universal symbol of plenty, peace and victory, has attracted the attention of President Reagan, who has given the gift pack to foreign dignitaries as an emblem of goodwill. TUNA MESSINESE (3 servings)

This tuna dish highly redolent of olives is from Franco Landini, who with his brother Piero owns La Lampara, an Italian seafood restaurant in Alexandria.

2 tablespoons olive oil

3 slices fresh tuna, 9 ounces each

Salt and pepper to taste

1/2 cup dry white wine

1 teaspoon capers

1 garlic clove, minced

2 cups chopped fresh plum tomatoes

1 anchovy, chopped

1/2 cup oil-cured gaeta olives

2 tablespoons chopped fresh parsley

Heat oil in a large skillet. Add tuna, sprinkle with salt and pepper and brown quickly on both sides. Add wine, capers, garlic, tomatoes, anchovy and olives. Cook 5 minutes over low heat. Sprinkle with parsley and serve very hot. MOROCCAN CHICKEN TAJINE WITH OLIVES AND LEMONS (6 servings)

1/4 cup olive oil

5 pounds chicken breasts or assorted pieces

1 1/2 cups minced onions

2 garlic cloves, minced

1 tablespoon paprika

1 1/2 teaspoons ginger

1/2 teaspoon turmeric

1/8 teaspoon saffron

Salt and pepper to taste

4 lemons

2 cups boiling water

1 cup small pitted green olives (spanish or calamatas)

Heat oil in a large skillet, add chicken and brown. Remove from pan. Reheat oil remaining in skillet. Add onions and garlic and brown lightly. Add paprika, ginger, turmeric, saffron, salt and pepper. Stir and cook 2 minutes. Cut lemons into eighths and remove seeds. Return chicken to skillet and add water and lemon pieces. Cover and bring to a boil. Reduce heat and simmer 1/2 hour or until chicken is tender. To remove excess salt from olives, place them in a saucepan with water to cover. Bring to a boil. Drain and repeat. Drain olives and add to chicken. Heat through. Serve over rice or couscous. TUNA TAPENADE (12 servings)

1 cup oil-cured black olives or more to taste, pitted

2 ounces anchovy fillets, soaked 1/2 hour in cold water to remove salt

7 ounces water-packed tuna fish

1/2 cup capers

4 cloves garlic, crushed

Pepper to taste

Juice of 1 lemon

1/4 to 1/2 cup olive oil

Place olives, anchovies, tuna, capers, garlic, pepper, lemon juice and 1/4 cup oil in the bowl of a food processor. Process until smooth, adding more oil as needed to make a not too thick paste. Serve as a dip for fresh vegetables or spread on bread or crackers. OLIVE BREAD (Makes 1 loaf)

In "The Book of Bread" (Harper and Row, 1982), Judith and Evan Jones describe an olive bread from Cyprus called eliopsomo, which also includes mint and onions for flavor.

1 tablespoon active dry yeast

1/2 teaspoon sugar

1 1/2 cups warm water

1/2 cup coarsely ground whole wheat flour

3 3/4 cups unbleached white flour

3 tablespoons olive oil

2 teaspoons coarse salt

1 small onion, chopped

2 teaspoons dried mint

12 black Greek olives, pitted and halved

Cornmeal

Dissolve yeast and sugar in warm water. Stir in whole wheat flour and 1 1/2 cups white flour. Beat at least 50 strokes, cover with plastic wrap and let stand for 1 to 6 hours. Stir all but 1 teaspoon of the oil into the dough with the salt, onion, mint and olives. Work in remaining white flour until it becomes hard to stir. Turn dough out onto a floured surface and let rest 5 minutes. Knead dough 8 to 10 minutes, adding more flour as necessary, until dough is resilient. Lightly oil the bowl, return dough to it, turning to coat, and cover with plastic wrap. Let rise until doubled, about 1 1/2 hours. Turn dough out, punch down and form into a large round loaf. Place on a baking sheet sprinkled with cornmeal. Cover loosely with a towel and let rise again until doubled in bulk, about 45 minutes.

Bake bread in a 425-degree oven for 15 minutes. Lower heat to 350 degrees and bake another 35 minutes. Brush with remaining olive oil and cool on a rack.