PreS-Gr 2 In one or two lines of text per page and large, boldly colored illustrations, Mercer tells the tale of a little boy who is sure that there is an alligator under his bed. Getting no sympathy from his parents who never saw it,'' he forms a plan of attack. He leaves a trail of food from his bed through the house to the garage door. He then follows behind as the alligator gobbles up the goodies, fresh vegetables, fruit, and eventhe last piece of pie,'' making its way to the garage. The boy then locks the door. The last page shows the note he leaves for his father, telling him that there's an alligator in the garage and to wake him up ``if you need help.'' Children will relate to this young hero's triumph over normal childhood fears, and they'll love his clever solution to his problem. The book gleams with crisp full-color watercolor illustrations, and the alligator has just the right touch of scariness. The little boy is obviously a child of the 1980s, with his hot wheels tricycle and robot transformer type toys, but the story is timeless. Sure to become as popular as Mayer's There's a Nightmare in My Closet (Dial, 1968) and bound to be a storyhour staple.Patricia Homer, Lowville Acad . , N.Y.