Local libraries are repositories of all manner of cookbooks--enough to satisfy the compulsive cookbook buyer, to be sure, but collections varied enough to inspire the novice and the faintly curious.

The Martin Luther King Library at 9th and G streets offers more than 3,000 cookbooks, according to Jim O'Neill, coordinator of the Adult Service for the District's public libary system. The D.C. system, consisting of 21 libraries, 4 storefront libraries and 2 kiosks, has collected 5,000 or so cookbooks, O'Neill estimates. All can be carried home at the flash of a library card or perused leisurely at the library.

Virtually every D.C. library has a copies of basic cookbooks, says O'Neill, including "Joy of Cooking" and the 1981 "Good Housekeeping" cookbook. Pretty books are the most popular, he says; the large, colorful, explicit Sunset books are recent purchases at King. Ethnic cookbooks, too, have a lot of appeal.

The District collection includes everything from M.F.K. Fisher's book of essays, "The Art of Eating," to 16 copies of Sunset's "Soups and Stews." At the King Library, there are shelves of books on special diets and special appliances. There are entire books dedicated to electric blenders.

Between the covers of these books lurk recipes that may be prepared in a hurry, such as the following, gleaned from the pages of library books. If you've spent too long at the library and need to rush home, you can make the following dinner after a quick trip through the express lane of the supermarket, provided you have flour, sugar, butter and/or oil, salt and pepper in the kitchen at home.

EXPRESS LANE LIST: fresh or frozen spinach, milk, nutmeg, thyme, potato, mushrooms, blueberries and cinnamon. SPINACH SOUP (4 to 6 servings) 2 pounds fresh spinach (or 20 ounces chopped, frozen spinach) 1/4 cup butter 4 to 5 cups milk 1/4 cup flour 1/2 teaspoon thyme 1/4 teaspoon nutmeg Salt and pepper to taste Sour cream (optional)

Clean and trim fresh spinach. Melt butter in large skillet and add spinach. Cover skillet and cook spinach about 5 minutes, stirring occasionally, until the leaves have wilted. (If using frozen spinach, place in saucepan with butter, cover and heat on low until spinach is thawed, remove cover and allow excess moisture to evaporate.) Place leaves in a blender and blend until smooth. Add 1 cup milk and flour and blend several seconds. Return spinach to skillet. Stir in remaining milk, thyme, nutmeg, salt and pepper. Bring to a boil and cook until thickened. Serve in hot bowls with filled baked potatoes to the side. Top with sour cream if desired. From Sunset's "Favorite Recipes for Soups and Stews" FILLED BAKED POTATOES (4 servings) 4 large baking potatoes 12 ounces mushrooms or 1/2 pound spicy italian sausage 3 tablespoons butter

Wash potatoes and place in 375-degree oven. Cook 60 minutes, piercing with fork after 45 minutes. Wash, dry and slice mushrooms. Saute' quickly in butter. If using sausage, break it up and brown it (without added fat) and drain well. Slice open cooked potatoes and fill with mushrooms or sausage. Adapted from "Good Housekeeping Cook Book" BLUEBERRY BETTY (4 to 6 servings) 1 pint fresh or frozen blueberries (substitute 2 cups canned, drained blueberries, or the equivalent of other fruit, such as sliced apples) 1 teaspoon lemon juice 1 teaspoon cinnamon 3/4 cup flour 1/2 cup granulated or brown sugar 1/3 cup butter Heavy cream or vanilla ice cream, optional

Place fruit in lightly greased 1-quart casserole and toss with lemon juice and cinnamon. Combine flour, sugar and butter, using a pastry blender or two knives to cut the butter in until the mixture resembles cornmeal. Sprinkle over fruit and bake at 350 degrees for 40 to 50 minutes. Spoon into bowls. Serve with cream, vanilla ice cream or plain yogurt, if desired. From "Meals in a Hurry," by Margaret Hoppel