Dav Pilkey. Scholastic/Blue Sky, $16.95 (144p) ISBN 0-439-04995-4

Fourth-grade cut-ups Harold and George and their principal-turned-superhero are as funny as ever in Pilkey's third Captain Underpants caper. (For those in the dark, the superhero in question is an underwear-clad, toilet-paper-toting crusader for "Truth, Justice, and ALL that is Preshrunk and Cottony"). As in the earlier installments, this zany tale adopts a variety of formats, including sprightly illustrated text; reproductions of the two boys' homemade comic books; and "flip-o-rama" pages that replicate "world-famous cheesy animation technique." Captain Underpants and his errant students here go up against a trio of aliens posing as lunch ladies. Suddenly students begin turning into "zombie nerds": "Look," says George, "They're all wearing broken eyeglasses held together with masking tape¦ and they've got vinyl pocket protectors!!!" It's all part of the aliens' quest to take over the world:"It won't be long now," says the evil Klax. "Tomorrow we'll feed them Super Evil Rapid-Growth Juice! Then they will grow to the size of Zleqxisfp trees." Those with a limited tolerance for the silly need not apply to the Captain Underpants fan club, yet its legion members will plunge happily into his latest bumbling adventure. Ages 7-10. (Sept.)