PARSLEY GETS by on its looks. From high school home-ec majors to Julia Child, cooks everywhere know those leafy green sprigs will dress up a blah-looking dish or cover up a downright disaster.

But parsley is far more than just a pretty plate. In addition to being an attractive, all-purpose garnish, it's a universal flavoring ingredient that's been around for centuries. In a cookbook written by the first-century gourmet Apicius, parsley is used in a highly spiced sauce for roast meat (along with other such ingredients as asafetida root, lovage and hazelwort).

European cooks have long used parsley to enrich sauces, soups and stews. It's one of three ingredients, along with bay leaf and thyme, in a bouquet garni, an herbal bouquet that is tied together in cheesecloth, then simmered in a sauce or stew to flavor it. French cooks use parsley as a primary ingredient in persilade. Combined with chopped garlic and buttered breadcrumbs, it is crumbled onto sauteed vegetables, massaged into roast lamb or spread on sliced left-over meat.

One of the most versatile uses of parsley is in maitre d' butter, a fancy finish for a steak, broiled fish, boiled potatoes or almost any vegetable. To make it, combine a stick of softened butter with a tablespoon or so of freshly squeezed lemon juice and 1 to 1 1/2 tablespoon of finely chopped parsley, or more to taste, salt and white pepper. Some cooks like to freeze maitre d' butter in tubes or blocks and then slice off whatever they need.

Parsley is also delicious stirred into scrambled-eggs or sauteed shellfish or tossed with salad greens, rice or pasta. (For an elegant first course or side dish, add chopped parsley and pine nuts to hot buttered pasta.)

And parsley is a stellar seasoning for one of summer's most appealing and colorful alternatives to the green salad: sliced, garden-fresh tomatoes and halved hard-boiled eggs with the yolks still a bit soft, drizzled with a mustard-spiked vinaigrette and sprinkled with chopped parsley.

Like rosemary, basil and dill, parsley is actually an herb, but unlike the others, it's almost always available fresh in the supermarket. The most common kind of parsley is the curly leaf variety, though some stores also carry Italian parsley, which has a flat leaf. Italian cookbook author Marcella Hazan says that Italian parsley has "a better developed, yet less pungent fragrance" than the curly variety. She adds that in most recipes, either kind will do.

When shopping for parsley, look for bright green leaves. Avoid yellowed parsley -- it's dry and old. To wash a bunch, place it in a colander and toss it with your hands under cold running water. Squeeze it lightly with paper towels, then place it in a plastic container and cover with a tight-fitting lid, or put it in a plastic bag, then tie shut securely and refrigerate. Properly stored, a bunch of parsley will stay fresh for 10 days or longer. Some parsley fanatics prefer to store it chopped, ready to be used at a moment's notice.

A surprising fact about this emerald green herb -- it's very nutritious. According to the excellent book "Fresh Food," parsley contains, per ounce, more vitamin A than carrots, three times as much vitamin C as oranges and twice as much iron as spinach. Popeye would have never left any on his plate.

Try the following parsley-flavored recipes, and neither will you. MUSHROOM AND PARSLEY TOPPING (4 servings) 2 tablespoons butter 1 tablespoon oil, preferably olive 1/2 pound mushrooms, sliced 1 clove garlic, minced 3 tablespoons finely chopped parsley 1 medium potato, chopped 8 to 10 ripe olives, coarsely chopped Salt and freshly ground pepper to taste

In a medium skillet, heat butter and oil. Add mushrooms and saute 5 to 6 minutes. Add remaining ingredients and continue to cook over low heat, stirring occasionally, for 5 to 6 minutes longer. Serve over broiled hamburgers, flank steak or chicken. PARSLEY POTATO SALAD WITH PROSCIUTTO (6 servings) 6 or 7 medium red potatoes (about 2 1/2 pounds) 6 tablespoons olive oil 2 tablespoons red wine vinegar 1/2 cup finely chopped parsley 3 tablespoons finely chopped scallions Salt and freshly ground pepper to taste 4 paper-thin slices prosciutto (about 1/8 pound), torn into small pieces

Boil unpeeled potatoes until tender, about 20 minutes.

Meanwhile, in a large bowl, mix oil, vinegar, parsley, scallions, salt and pepper.

When potatoes are tender, drain and cool just enough to be handled. Peel and cut into 1/2-inch thick slices. Put into bowl with dressing, add prosciutto and toss lightly. Serve while still warm. BROILED FILLETS WITH PARSLEY-PARMESAN BUTTER (6 servings) 6 fish fillets, about 1/3 pound each 1 stick butter, softened 2 tablespoons finely chopped parsley 1/3 cup parmesan cheese 2 teaspoon capers, optional 1 teaspoon French-style mustard Juice of 1/2 lemon Few drops worcestershire sauce

Preheat broiler. Line broiler pan with aluminum foil and brush lightly with cooking oil. Place fillets in pan skin-side down.

With a fork, whip butter until soft. Add a remaining ingredients and mix well. Spread on fillets and broil, 5 to 6 inches from heat, for 6 to 7 minutes. Serve garnished with thin lemon slices each topped with a mound of finely chopped parsley.

This butter mixture is also delicious on broccoli, green beans, cauliflower and other vegetables.