If onlym - that's my recurring response to this collection of mysteries. If only writers would let their teen-age detectives talk and act like they were 12 or 13 instead of 55. If only they'd drop the silly characters in favor of some plots to really test their readers' intelligence and perception. If only books for teens and pre-teens matched their counterparts for younger readers.
The stand-out book of the lot is a success because it's about a believable family with believable youngsters. Zilpha Keatley Snyder's The Famous Stanley Kidnapping Case (New York: Atheneum, 212 pp., $2.95, paperback) is set in an Italian villa where an American professor, his artistic wife, and their five children are living during a sabbatical year abroad. Because author Snyder knows how real kids think and react, she can confidently turn her characters loose to their own worlds of imagination.
The children's adventures have a fine balance of humor and danger. One day they're learning how to count out the thousands of lire it takes to buy anything , and the next they've been kidnapped and are being held for ransom in a dingy cellar. It's a threatening predicament, but the kids pull through with the help of a bathrobe belt and - but that would be giving the plot away. Although there's not much mystery here, it's the scary-entertaining kind of book that should appeal to teens and some younger readers as well. What they'll learn about Italy comes as a bonus.
The editors at Simon & Schuster's Wanderer Books, which publish the Nancy Drew, Hardy Boys, and Bobbsey Twins series, could take some lessons from Ms. Snyder. If The Sinister Omen by Carolyn Keene (illustrated by Paul Frame, 205 pp., $2.75 paperback) and The Voodoo Plot by Franklin W. Dixon (189 pp., $2.75 paperback) are representative of the kinds of adventures Nancy Drew and the Hardy Boys are up to today, preteen readers are in for a big yawn. Stilted dialogue and monotonous ''would you believe it?'' twists of plots unfortunately characterize both books.
There's a wonderfully crusty old lady involved in Nancy Drew's attempts to round up a gang up stamp thieves, but ''The Sinister Omen'' doesn't have much else going for it. From the moment a decal of a black vulture appears on the rented seaplane she's piloting, you know you're in for one crashlanding after another. Nor do the Hardy Boys fare much better. As they schlep from a snake-infested swamp to New Orleans during Mardi Gras, ''The Voodoo Plot'' grinds along at the pace of a tired serial whose writers seem interested only in churning out their quota of words.
Thankfully, the Bobbsey Twins emerge with some spunk intact. Not only is there excitement and tension in their sleuthing, but readers of The Camp Fire Mystery by Laura Lee Hope (illustrated by John Speirs, 126 pp., $2.75 paperback) also learn a good bit about ballooning and children with physical handicaps. Just enough clues are dropped along the way to keep the pages flying, and the conclusion comes as - what's this? - a surprise!
Equally lively is Constance Layman's The Great Pistachio Case (New York: Simon & Schuster. 139 pp. $2.50). Although the premise sounds silly - a hunt for a gang of pistachio-nut thieves - the humor is delightful. Granny Graham, owner of the J. G. Detective Mail-Order Agency, is a splendid foil for the formidable Mrs. Ophelia Phinney, and the kids she deputizes are just as outrageous. When several young ladies are pressed into front-line service on the town's losing football team, how they save the game of the year is matched only by the detective skills they display off the playing field.
By comparison, the three teen-age boys who star in William Arden's The Mystery of the Purple Pirate (New York: Random House, 151 pp., $1.95) come off as insipid bench warmers and the plot plods. There are some intriguing clues along the way, but who's going to stay with the action long enough to put them together?
Sid Fleischman's The Case of the 264-Pound Burglar (New York: Random House, 62 pp., $1.50.) is a welcome addition. In this easy-to-read book about the Bloodhound Gang of Children's Television Workshop fame, there are plenty of lively characters to keep younger readers coming back for more adventures. Just as bright are Crosby Bonsall's two new ''I Can Read'' mysteries: The Case of the Double Cross (64 pp., $2.95 paperback) and The Case of the Dumb Bells by (64 pp. , $2.95 paperback, both published by Harper & Row in New York). Zany illustrations and quirky kids should make fast friends of beginning readers.