It may be that for the moms of yore there was no greater reward than to watch the family demolish one of her apples pies. These days there are other rewards, the kind that can be won in recipe contests.

Take, for example, Kitty Castagnetti of Long Green, Md., north of Baltimore. She received a $100 savings bond, a spice rack complete with 21 spices, three cook books and the electric frying pan she used to prepare the first place recipe at this year's "Magic With Oysters" cooking competition. The event was part of the Chesapeake Appreciation Days.

Castagenetti had been one of the five finalist in 1977, but she didn't qualify last year. On the day before this year's entry deadline she "had bought the oysters but was trying to think of a different way to prepare them. It seemed everything had been tried. Then I thought of mushrooms. Crab is good with mushrooms, so I tried them with oysters on my family. My husband is my severest critic. When he liked them, I felt I had it made."

She did.Her recipe follows. KITTY CASTAGENETTI'S OYSTER STUFFED MUSHROOMS (Makes 15 to 24, depending on size) 1 pint stewing oysters, drained (reserve liqueur) 1 pound large mushrooms, washed, dried and stems removed 2 tablespoons cooking oil 2 tablespoons butter or margarine 6 cloves garlic, peeled and minced 1/2 teaspoon seafood seasoning 1/2 teaspoon oregano 2 tablespoons chopped parsley 1/2 teaspoon lemon pepper 1/2 cup seasoned bread crumbs Parmesan cheese

Slice mushroom stems. Heat oil and butter in a frying pan. Add garlic and stems. Cook until tender, then add drained oysters, seafood seasoning, herbs and pepper. Saute to blend flavors, then add about half the reserved oyster liqueur. Heat to a boil, then transfer contents of pan to a mixing bowl. Add bread crumbs, mix and set aside.

Place mushrooms caps in pan, cavity side up. Heat for about 5 minutes, or until caps are tender. Remove from heat. Fill each cap with oyster mixture, sprinkle with cheese and return to heat until cheese blends with filling. Serve hot. (If not participating in a contest, the last part of the recipe may be done in a 350-degree oven.) Allow three mushrooms for an appetizer serving, five or six for a main course.

Another woman who did well in a recent cooking competition was Darlene Kenworthy of Chantilly, Va. She reaped a cookbook, potholder and apron when her "economical energizing sandwich" recipe was judged best of all entries in the Brown Bag category of a nationwide contest for employes of Kelly Services.

She explained that taking a sandwich to work wasn't just an economy move for Kelly employes. "Working as a temporary you never know what you will find," she said. "In some offices there are cafeterias, in others only vending machines.Some regularly go out for lunch. Some don't take a lunch break at all. You never know."

Kenworthy makes her sandwich spread in quantity and uses it as needed, sometimes serving it at home on lettuce as a salad rather than in a sandwich. But despite the success of the recipe, she is not a compulsive brown bagger. Her children, ages 8 and 10, buy their lunch at the school cafeteria. "I can't stand making sandwiches every day," she said. DARLENE KENWORTHY'S ECONOMICAL ENERGIZING SANDWICH (Makes 6 sandwiches) 2 hard-cooked eggs, mashed 1 can (6 ounces) flaked tuna, drained 1/4 cup grated carrots 2tablespoons chopped onion 1/4 cup chopped celery 1teaspoon finely chopped green pepper 1/4 cup chopped peanuts or cashews 1/3 cup mayonnaise 1 teaspoon curry powder Salt and pepper to taste 1 leaf lettuce or spinach per sandwich Bread

Mash the eggs in a medium mixing bowl. Add tuna, carrots, onion, celery, green pepper and nuts. Stir until evenly distributed. Blend curry powder into mayonnaise. Add tuna mixture. Spread onto butteered bread or buns and chill overnight in refrigerator. Add lettuce just before eating.