In the all-important matter of the cooky, we Americans have been most extraordinarily inventive. Hermits, wafers, rocks, snickerdoodles, pillows, fingers, cobblestones, aggies, and pinwheels are all part of Maida Heatter's marvelous selection which also includes assorted European thefts and borrowings--Italian neapolitans, classic Viennese crescents, and Scottish caraway crisps. Heatter is both an orderly and a relaxed teacher, and nothing here is made to sound forbiddingly difficult. The cookies are grouped into five main classifications (drop, bar, icebox, rolled, and hand-formed), with the more essential kitcheny descriptions (""chewy,"" ""very chocolatey,"" ""candylike"") also given. Here are cookies for hanging on the Christmas tree, cookies for ""natural food"" eaters, cookies with fruit filling and cookies with icing, and five kinds of brownies. The recipes all make generous batches and only a miscreant could be indifferent.