More a product of corporate public relations than creative programming, "Sign-On," the pilot for a "proposed innovative" children's series from CBS, airs at 4 p.m. today on Channel 9. Networks love to brandish these proposed shows as evidence of their commitment to worthwhile children's fare, but the worthwhileness of "Sign-On" tends to get lost in a welter of clatter.

Produced by the Children's Television Workshop of "Sesame Street" fame, the half-hour hodgepodge of fact and frolic gets off on four wrong feet with two jolly jump-ups assigned as co-hosts: Steve McNaughton ("Susan, I think we have a terrific show today, don't you?") and Susan Spilker ("I know we do!"). They're not much less bubbly and burbly than Pinky Lee was three decades or so ago.

Later, though, Spilker hunkers down for a serious chat with pubescent girls who fear they are going to be flat-chested for the rest of their lives. Susan was flat-chested, too, she says, and concludes the segment with the straight-faced adviced, "You just hang in there."

Other segments include an animated sign painter; a news feature on a Duluth, Minn., project to discourage student shoplifting; a song by the co-host (they try the we're-all-in-this-together soulmate stance of Alex and Annie on ABC's "Kids Are People Too"); and an informative interlude, produce by CBS News, about fancy scoreboards at ballparks.

Considering that a second episode of "Sign-On" has not been, and may never be, scheduled, it seems unfair to end a dramatic vignette, "Welcome to Twin Oaks," with a teasey "To Be Continued." The attractive actress playing the mother in this sketch is Elinor Donahue, once daughter Betty on the fondly remembered sitcom, "Father Knows Best."

Networks flaunt projects like this in their corporate advertising and when representatives are called before congressional committees. In fact, a previous CBS project, "On the Road," has been at best an occasional feature. NBC launches its prime-time "Project Peacock" children's series this Sunday, but in the suicidal time slot opposite "60 Minutes" on CBS. "Sign On" radiates good intentions which, put up against the hours of cheap cartoons and kid-oriented pap aired weekly on CBS and the other network, amount to not even the first plateau on a hill of beans.