No author writes funnier books for children than Pinkwater. His latest exploration of incongruity involves Mozart, a Clouseau-like French detective, and an extraterrestrial muffin thief who plans to use the muffins to fire a rocket and return home. Don Pastrami, the thief, "". . .appeared to be human,"" says Inspector LeChat. But ""So do a lot of people,"" says the famous detective, Mozart, who also happens to be a well-known composer and to hold the world record for the number of muffins consumed by a human in a day. Fol. lowing the Don to the Vienna Woods, Mozart engages in operatic dialogue with him and explains that he knew he was from outer space because no one on Earth would eat a Gorgonzola muffin. Silly, full of sly references, language so artfully and rhythmically arranged it seems choreographed. Pinkwater's illustrations, apparently based on computer graphics, add an appropriately zany touch. Should be popular with young readers for both its brevity and its wit.