Rod McLeish, the journalist and novelist whose commentaries are broadcast on the CBS Morning News, is an enthusiastic cook. He collects recipes and cooking tips as carefully as he weighs both sides of foreign policy conflicts. When in doubt, he improvises. Here are two of his recipes that helped make a success of a recent dinner party. ROD MACLEISH'S CHICKEN AND SHELLFISH (Serves 8) 8 chicken breast halves, boned and skinned 5 tablespoons butter 12 small new potatoes, peeled 1 pound shrimp, shelled and cut in half 1 pound scallops, cut in half if sea scallops 1 pound mushrooms, coarsely chopped Tarragon to taste Salt and pepper to taste 2 quarts (about) fish stock* Pinch mace (optional)(FOOTNOTE)

* As a substitute for fish stock, use 2 cups dry white wine and 2 cups clam juice. To make the stock, saute 2 cups minced vegetables (onion, carrot and celery) in 3 tablespoons butter. When they have softened add 2 pounds of fish frames, 1/2 teaspoon thyme, 3 or 4 sprigs parsley and a few grinds of pepper. Pour in 2 quarts water (or half water and half wine). Bring to a boil, skim off scum and simmer, partially covered, for 30 minutes. Strain off liquid. (END FOOT)

Heat 3 tablespoon butter in a skillet. Brown chicken breasts lightly on both sides. Remove. Spread remaining butter over bottom and sides of a Dutch oven. Make a layer of chicken breasts. Ring this with potatoes. Scatter shrimp, scallops and mushrooms in center and sprinkle with tarragon, salt and pepper. Repeat, making one or two more layers.

Add fish stock to just cover ingredients and bring to a boil. Lower heat to a simmer and cook, covered, for 30 to 40 minutes, or until chicken is cooked through. Arrange solid ingredients on a serving platter and keep warm. Pour off half of cooking liquid and reserve for another purpose. Taste remaining liquid, adjust seasoning as desired and thicken over heat with a mixture of 4 tablespoons butter and 4 tablespoons flour, stirred in by small chunks or 4 tablespoons arrowroot dissolved in cold water. Pour some over serving platter, pass remainder as needed in a gravy boat. ROD MACLEISH'S APRICOT DESSERT (Serves 4) 2 cans (8 ounces each) apricot halves, drained 1 package (4 ounces) dried apricots 1/4 cup orange liqueur Freshly grated nutmeg 8 ounces whipping cream 1 tablespoon orange liqueur

In a blender, food mill or food processor, puree drained apricot halves. Chop dried apricots very fine. Transfer both to a mixing bowl. Stir in orange liqueur and nutmeg to taste. Fill large long stemmed glasses or dessert cups two-thirds full with the mixture. Whip the cream lightly, spoon it atop the apricot mixture; grate a little nutmeg over each portion and refrigerate for at least 2 hours before serving.