"The Idolmaker" stands apart from this season's glut of appalling or dumbfounding entertainments. It's one of the few new American movies to promise patrons a pleasant and even illuminating time.

The film, which opens today, is a fictionalized dramatization of the career of Bob Marcucci, the Philadelphia songwriter and promoter who engineered the teen-crush singing careers of Frankie Avalon and Fabian in the late '50s and early '60s.

From "Nashville" through "Coal Miner's Daughter," pop music has become a more reliable source of human interest than any other "authentic" subject American filmmakers seem attracted to. "The Idolmaker" is no exception. It was evidently developed at the urging of Marcucci himself, but who ever said the movies could do without self-promoters and go-getters? Marcucci was correct in thinking of himself as a promising subject.

Ray Sharkey, energized but unglamorous, seems an astute choice for the fictional go-getter, Vinnie Vacarri, based in Brooklyn and envisioned as a frustrated performer who attempts to realize himself by training and managing young men who might project charismatic appeal while crooning love-sick ballads to a public dominated by adolescent girls. A trend-watcher and anticipator, Vinnie is looking for Italian-American kids who can embody a wholesomely swarthy image -- dark, cute, sexually stirring and yet, when all is said and done, unthreatening to girlish psyches.

His first prospect is a raffish young musician, Tommy, who plays saxophone with a jazz band at a club in New Jersey. Vinnie streamlines his appearance, imposes a synthetically polished singing style, hustles upstate disc jockeys and Manhattan fan magazine editors and struggles to prevent Tommy, now known professionally as Tommy Dee, from losing interest or doing anything scandalous. Vinnie and Tommy combine to snatch triumph from the jaws of disaster at a sock hop in Rochester, and the act is off and running. Tommy really triggers something in the teenyboppers, and Vinnie proves his ingenuity and determination as a promoter. Tommy emerges as a pop recording star.

Content at first to manage Tommy's career, Vinnie begins toying with the idea of a fresh challenge. Tommy began with some raw musical talent, which Vinnie proceeded to refine and stylize. What if he stamped the Vinnie Vacarri style on a totally unformed personality? Wouldn't the achievement be far more impressive?

He fixes on a shy, proud kid employed as a waiter in his brother's Italian restaurant. The new prospect is dubbed Caesare and subjected to the intensive Vinnie Vacarri course in silky-smooth sex appeal. Vinnie's aim is to spring Caesare in one overwhelming concert date after a prolonged advertising tease. His relationship with Tommy begins to fray as he devotes more time to Caesare. Although the caper proves a success, Vinnie eventually loses both his proteges as their popularity increases and the conficts between manager and performers intensify.

In the spirit of Vinnie himself, director Taylor Hackford and screenwriter Edward Di Lorenzo have contrived to improve on the period and pop music figures they're dealing with. The movie seems a reasonably accurate reflection of the Frankie Avalon-Fabian phenomenon, seasoned with plenty of sardonic humor and inside dope. At the same time, Paul Land and Peter Gallagher, the young actors cast as Tommy Dee and Caesare, respectively, project so much more personality and drive than their real-life prototypes ever did (at least in the presence of a movie camera) that we seem to be dealing with a bigger phenomenon altogether. The suggestions that Vinnie messes up by acting dictatorial never take root, because it always looks as if these young men will outgrow and defy him once they become confident of their own performing powers. If anything, his instinct for talent has been too good for his own good.

The script fails to assimilate a romantic subplot in which Tovah Feldshuh plays a magazine editor who consorts with Sharkey. As a matter of fact, her principal function is to nag at him for real or imagined shortcomings in his dealings with the boys. After setting a crisp, informative pace for a good three-quarters of the film, the script also seems to run out of gas in the closing stages, a flaw it shares with both "The Buddy Holly Story" and "Coal Miner's Daughter."

Fortunately, Sharkey brings off a difficult lyric assignment that gives the story an emotional lift at the fadeout. After several years in retirement, Vinnie decides to have a go at singing himself. Sharkey puts across his song, "I Believe It Can Be Done," on sincerity; his voice is an extremely limited instrument, and yet he gets a gallant, touching kind of expression out of its very fragility. It's not unthinkable that Vinnie could bounce back doing his own songs, and it's agreeable to imagine that he does.

Like Steve Rash on "The Buddy Holly Story," Taylor Hackford finesses a tight budget by combining great affection for the material and performers with considerable pictorial discipline and ingenuity. There's rarely wasted space or movement in the film. In particular, the performance scenes (Jeff Barry has composed 11 new songs that evoke the pop sounds of 20 years ago) evoke a wonderful feeling of immediacy in a variety of settings, from the smoky close quarters of the jazz club to a giant auditorium in Memphis. Nice work if you can get it, and "The Idolmaker" is a very nice job of thrifty, emotionally committed filmmaking.