"The Slipper and the Rose," which slipped into a few area theaters last weekend, won't be remembered as one of the great musicals, but it's more diverting than I supposed. Judging from the abrupt, unannounced local opening, Universal may be giving the film a brush-off in general domestic release, although it was conceived and initially touted as a prestige production for the family trade, which would seem to have no cause to reject it out of hand. "Slipper" may not be a world-beater, but it's a considerable improvement on the likes of "Bugsy Malone" and "Quilp."

Bryan Forbes has never directed a musical before, and his inexperience probably accounts for the stilted notion of picturesqueness that often substitutes for genuine lyrical flair and inspiration. He seems to be influenced by an admirable model, Carol Reed's film version of "Oliver!," where prettiness and moodiness were exquisitely blended. White he evidently lacks the knack, and perhaps the ingredients, for a comparable blend, Forbes is fitfully succesful in attempting to do something pretty and ingretiating.

Richard M. and Robert B. Sherman, the American team best known for "Mary Poppins," wrote the score for "Slipper" - I'm not sure where that rose is supposed to come in - and colaborated with Forbes on the screenplay. They've transposed the Cinderella story to a minuscule Middle European kingdom, Euphrania, in the late 18th century.

Since Gemma Craven's Cinderella belongs to the Euphranian gentry and Richard Chamberlain's Prince seems patriotically obliged to marry a foreign princess for the sake of his vulnerable little fatherland, the filmmakers end up outsmarting themselves by complicating the romance unnecessarily. "Slipper" would be tidier if Cinderella and the Prince didn't have to face even greater obstacles after being reunited.

The script does have agreeable outbursts of silliness and fancy. Michael Horden as the worried, abstracted king and Annette Crosbie as Cinderella's brisk, humorous fairy godmother are consistently delightful. The Shermans have become faily expert at fairy godmothers, and Crosbie projects a vivacious matter of factness about magic that is quite irresistible.

Although Horden and Crosbie enjoy the wittiest opportunities and emerge as the class of the show, Margaret Lockwood shows surprising force of personality in the role of Cinderella's stepmother and Kenneth More has some pleasantly goofy moments as the king's chief adviser, especially when he wears his frizzy "formal" wig. Forbes has also made it possible for the late Edith Evans, whom he worked with several times to go out in comic glory as the down queen, whose senile interjections are often peculiarly penetrating.

Cemma Craven, a young Irish singer-across making her film debut, seems a rather zaftig vision of Cinderella, who might be more transporting photogenically if embodied by someone on the tradition of Audrey Hepburn in "Roman Holiday." There's not a trace of fragility about the sturdy, sweet-voiced Craven, who suggests a healthy milkmaid and looks charmingly similar to the young Jane Fonda whenever she smiles.

Craven and Chamberian don't exactly harmonize as fairy-tail lovers, but I'm not sure who could harmonize with Chamberlain. At least her aura of freshness and wholesomeness seems to balance his aura of effects snobbery or whatever-it-is. Charmberlain impersonates the Prince satisfactorily, given the indignity of playing such sappy opertta heroes in the first place, and his singing has certainly come a long way since that unforgetable strangled rendition of the "Dr. Kildare" theme, "Three Stars Will Shine Tonight," which seemed to be recorded by a boy whose voice was changing.

The Sherman score, banal but serviceable, is aided immeasurably by Angela Morley's lush orchestrations Chamberlain and Christopher Bable, who plays his companion-at-arms, get one faily playful novetly number in which they frolic about the royal mausoleum. "Protocologorically Correct," a novelty promenade around to cabinet table led by Hordern and More, is a kind of old codgers' variation on the Shermans' standard word-game number. It's not likely to supersede "Supercalifragilistic . . .," camped-up charm as rendered here.