Robert Newton Peck's 33rd volume is wonderful fun. It is also the sixth book to feature the inimitable heroes Soup and Rob - a twosome with whom any kid (or former kid) who's ever had a bestm best friend can identify.
In this volume, the discovery of an old saddle in the loft of a neighbor's barn is only the beginning of a series of adventures in the town of Learning, Vt. For even this discovery pales beside the news that their beloved Miss Kelly, who has taught in the one-room schoolhouse for 30 years, is to be honored with a parade, complete with a brass band and ''Vermont's favorite singing cowboy, Hoot Holler.''
Then comes the horrifying news that the tribute to Miss Kelly may be ruined by Dr. Elsa Pinkerton Uppit, ''an extremely large woman, with flaming red hair and a very unpleasant face.'' This educational bureaucrat is the sworn enemy of all of Vermont's one-room schools and also dislikes older teachers. It remains for Soup and Rob to help save the day in a way that only they can.
The key to the book's appeal is author Robert Peck's deft characterization. The cast may seem somewhat stock. But it calls up instant images of a similar bunch at the Number Nine School in Salem, N.H., some 25 years ago - although our school had been converted from a two-roomer about four years before I arrived.
Fairly simple reading, ''Soup in the Saddle'' nonetheless has a lot to offer. It's the kind of book that may even tempt nonreaders. Even though most young readers won't have experienced a one-room school, they'll have no difficulty in identifying with the engaging heroes and sharing in their good-natured exploits.