Grapefruit can mean more than the dreaded main course on dieters' breakfast plates. Served as aperitif or dessert, grilled, in salads or made into drinks, jams and jellies, it can enliven any meal.

Its tart, yet slightly bland flavor makes it a delightful accompaniment for pork. Grapefruit brightens up a simple green salad; mixed with shrimp or crabmeat and a special dressing, its sections are attractive served in their scooped-out shells. The fruit combines well with slightly sweet salad dressings, and--surprisingly--with tart dressings as well.

When buying grapefruit, keep in mind that the most desirable fruits are thin-skinned and heavy. Some varieties may weigh over a pound each, but do not overlook the bargain to be had in smaller, good-quality fruit of uniform size.

In addition to fresh grapefruit, don't overlook canned grapefruit sections and juice, frozen grapefruit juice concentrate, jams, jellies, marmalades, ices and candies when planning menus. FRESH GRAPEFRUIT MOUSSE (4 to 6 servings) 1 to 2 grapefruit 1 envelope (1 tablespoon) unflavored gelatin 3 tablespoons cold water 1/2 cup whipping cream 2 eggs, separated 1/4 cup sugar 2 tablespoons honey 2 tablespoons orange-flavored liqueur Toasted sliced almonds

Segment and juice grapefruit to make 1 1/2 cups. Blend grapefruit juice and segments in blender or food processor; set aside. Dissolve gelatin in water; set aside. In a 2-quart enamel or stainless steel saucepan, scald cream. Combine egg yolks, sugar and honey. Gradually stir yolk and gelatin mixtures into cream. Cook and stir over low heat until mixture coats spoon, 4 to 5 minutes (be careful not to boil). Remove from heat. Stir in blended grapefruit and liqueur. Chill about 1 hour until mixture is slightly thickened, stirring once or twice. Beat egg whites stiff. Stir grapefruit mixture; fold in egg whites to blend thoroughly. Chill until set, about 3 hours. Sprinkle with almonds just before serving. BROILED GRAPEFRUIT (2 servings) 1 grapefruit, halved 2 tablespoons honey Cinnamon to taste Butter

Loosen sections of each grapefruit half with a sharp knife. Spoon 1 tablespoon honey over each half. Sprinkle with cinnamon and dot with butter. Place grapefruit under broiler 5 to 8 minutes. SEASHORE SPECIAL (4 servings) 1/4 cup butter 1/3 cup thinly sliced scallions 3/4 cup unseasoned dry bread crumbs 1 tablespoon lemon juice 1/2 teaspoon salt Dash liquid hot pepper sauce 1/4 teaspoon tarragon 4 fish steaks, each 1/2-inch thick or fillets, 1 1/2 to 2 pounds (salmon, halibut, sole, cod, haddock) 2 to 3 grapefruit

In small skillet, melt butter; saute' scallions until limp. Add bread crumbs; cook and stir 2 minutes. Add lemon juice, salt, pepper sauce and tarragon; cook and stir 2 minutes. Remove from heat; set aside. Arrange fish in shallow baking pan. Juice enough grapefruit to make 1/2 cup; pour over fish. Bake in center of 425-degree oven 10 minutes. Baste with pan juices. Cover fish evenly with crumb mixture. Bake 5 to 10 minutes longer, until fish flakes easily. While fish bakes, divide remaining grapefruit into segments to make 2 cups. Serve fish on platter surrounded with segments. GRILLED GRAPEFRUIT WITH KIRSCH (8 servings) 4 grapefruit, halved 1 cup sugar 1 cup kirsch Mint sprigs (optional)

Cut center out of each grapefruit half and loosen sections with sharp knife. Sprinkle each half with 2 tablespoons sugar and 2 tablespoons kirsch. Broil 4 inches from heat 5 to 8 minutes or until bubbly. Garnish with mint sprigs. CITRUS CHICKEN SALAD (4 servings) 2 whole chicken breasts, cooked, skinned and diced 1 grapefruit, peeled and sectioned 2 large oranges, peeled and sectioned 1 cup chopped celery 1 small bermuda onion Thinly sliced romaine Watercress For the dressing: 1 cup salad oil 1/2 cup catsup 1/3 cup vinegar 2 tablespoons sugar 1 teaspoon salt 1/2 teaspoon grated onion 1/3 cup chili sauce 1/4 cup chopped pimiento 3 teaspoons poppy seed

Carefully clean all membranes from citrus sections. Tear romaine into bite-size pieces; break watercress into small sprigs. Toss all ingredients together in a bowl. Fill scooped-out grapefruit halves with salad mixture.

To make the dressing, beat ingredients together in order listed. Store in covered jar. Shake well before serving on top of chicken salad. ENDIVE-GRAPEFRUIT SALAD (2 to 4 servings) 3 cups belgian endive, cut 1/2 cup grapefruit 1/2 cup strawberries 1/2 cup cherry tomatoes 1/2 cup kumquats 1/2 cup watercress leaves For the dressing: 1 egg yolk, lightly beaten 1 1/2 tablespoons lime juice 5 tablespoons oil 1/4 teaspoon salt

Cut endive into rounds. Peel grapefruit, remove membranes and cut in pieces. Cut strawberries and tomatoes in half. Cut kumquats in half and remove seed. Mix fruits and vegetables.

Combine egg yolk, lime juice, oil and salt and toss with salad. Serve on top of watercress leaves. MINTED GRAPEFRUIT-ORANGE (4 servings) 2 grapefrui, chilled 6 oranges, chilled 1 1/2 tablespoons sugar 1 1/2 cups mint leaves 2 1/2 tablespoons lime juice 1/2 cup fresh orange juice

Peel fruit and remove membranes, Slice, remove seeds and place slices in bowl. Sprinkle with sugar. Gently stir in mint leaves. Add lime juice and orange juice. Let stand 5 minutes before serving.