ROCKUMENTARIES have previously followed a rock band at its apex ("Mad Dogs and Englishmen") or at its collapse ("Let It Be," "The Last Waltz").

Director Michael Apted's "Bring On the Night" purports to give us something new: the birth of a band and a new music -- in this case Police captain Sting's jazz-tinged solo outing.

But however entertaining this "Night" often is, it is also too obviously a 97-minute advertisement for Sting's solo album, and falls short of being a convincing portrait of either the music or the musicians.

In the behind-the-scenes stuff, Apted gives us glimpses of the elation and banality involved in the pop star's latest turn. The music, appealing but hardly new, is a mix of conglomerate rock and electronic jazz, meticulously crafted by an ace band of all-black jazzers, borrowed from Weather Report and the Miles Davis and Wynton Marsalis ensembles.

But it don't mean a thing if it ain't got that Sting. In Apted's "candid" interviews, Sting is playing the actor as much as in "Plenty" or "The Bride." Photographed in moody, matinee-idol half-shadow, he's all studied self-deprecation and restraint. In this self-celebratory movie, he wants to be seen as the severe young schoolmaster guiding his high-spirited charges, or as the altruistic rock philosopher. By the end, we've had a bit too much of the good Sting, and the interviews with the other musicians are similarly stilted and self- conscious.

Apted does catch some vividly spontaneous moments: While the band is rehearsing in its rented chateau near Paris, an elderly tour group shuffles through; another time the band breaks into a whimsical jam on the theme from "The Flintstones." And in a novel use of montage, Apted traces several songs from composition on a computer keyboard to their gemlike concert versios.

TAKE 002397 PAGE 00002 TIME 14:57 DATE 11-07-85 In addition to the band's genesis, we have the dubious privilege of witnessing the birth of Sting's son. The graphic delivery-room footage, set to Sting's somber, didactic "Russians," is inappropriately intimate.

But when the band is literally unveiled for the climactic debut concert, it all comes together. And though Apted cuts away too often for audience reaction, the music does the talking -- and it is frequently rapturous.

BRING ON THE NIGHT (PG-13) -- At the West End Circle, Showcase Fair City and NTI White Flint.