EVERY once in a while a show comes along that reminds you of TV's potential for helping kids. It almost always happens on public TV, since broadcasting's duty to the young has been historically slighted by commercial stations and largely ignored by government agencies.
The show in question is not always a watershed event, and it isn't in the case of ''The Magic School Bus,'' a weekly science adventure program -- with the stress on ''adventure'' -- premiring Sunday (check local listings). But that show is PBS's first fully animated series, and it represents something all too rare on broadcast TV these days: a lively teaching tool that manages to be modestly entertaining as it informs.
Based on the Scholastic Books series by Joanna Cole and Bruce Degen, the 30-minute feature uses the school bus of the title to take a classroom of kids on hair-raising fantasy trips, fact-laden field trips of the imagination -- to places like outer space and inside the human body. In the first episode, a boy named Arnold is bugged at school by his know-it-all cousin Janet. Arnold is usually scared stiff at the prospect of the magic bus's wild treks, but to prove something to Janet, he finally gets the teac her, Ms. Frizzle, to turn the bus into a spaceship for a tour of the solar system.
Ms. Frizzle is only too willing, since half the format rests on her manic penchant for taking kids where the action is instead of merely telling them about things. ''Please let this be a normal field trip,'' Arnold says at one point. ''With the Frizz?'' his classmates respond. ''No way.''
Ms. Frizzle's voice is supplied by Lily Tomlin (many of the voices belong to well-known performers) and her comic energy and intelligence are part of the program's main appeal: a tone of risk-taking in pursuit of knowledge, a call to kids to drop their fears and plunge into the quest. The new show may not have quite the Elizabethan love of words for words' sake that the ''Electric Company'' did on PBS, or the magic (despite its title) of ''Sesame Street.'' But it does have that same heady feeling of absorb ing new ideas. You hear it not only in Tomlin's voice as she blithely plunges her students into strange new worlds, but also in the excited reactions of the class and the students' pointed questions as they encounter planets in the solar systems -- or, in later episodes, sound waves and predatory animals. The impact is positively exhilarating when the kids and Ms. Frizzle visit Mars and leap off a steep cliff, crying out in delight and discovery as they float down in the lesser gravity of that planet.
You also feel that vibrancy in the animation itself. The images are almost Grandma Moses-ish in their folksiness, yet the action is fast-paced, like commercials or music videos -- mercurial, excitable, impatient with the status quo and ever ready to interrupt and cut to the next scene. Sometimes the screen is a kaleidoscope that fragments into scattered dabs of color, then re-forms.
Although Ms. Frizzle is up front about her true intentions as a teacher, the show makes its points without being ponderous. It may not slip lessons in sideways, with the almost subliminal indirection of ''Sesame Street,'' yet ''The Magic School Bus'' gets so involved in the moment at hand that a young viewer's absorption of facts is a side effect. In the first episode, when the kids are on Venus, they ask what the clouds are, and Ms. Frizzle answers sweetly, ''They're deadly poison,'' providing a scary lesson in planetary weather.
In the fifth episode, a cat's huge head thrusts between grass blades and stares at the mouse-sized humans that have been miniaturized in one of Ms. Frizzle's crazy projects. ''Let's get out of here!'' yell the kids when they see the cat, in a chorus that harks back to Pinocchio's shout when the whale prepares to swallow him. But Ms. Frizzle, an eccentric sorceress, pets the huge cat's head and starts discussing its predatory behavior.
At the end of an episode, kids would no doubt find they had learned a lot if they stopped to check. They won't. The magic school bus is too much fun for that.