At its best, "My Bodyguard" recalls the freshness and authenticity of "Breaking Away" -- and for a while seems that it is going to be even better. That impression proves premature. After building up to a stirring, climactic turning point, Alan Ormsby's original screenplay falters in the stretch.

But by that time the movie has built up such a reserve of human interest and good will that nothing can erase the favorable impression left by Ormsby's tangiest scenes, Tony Bill's admirably steady and transparent direction and by the performances of the three young leads -- Chris Makepeace, Alan Baldwin and Matt Dillon.

Ormsby has focused on two aspects of school life that are seldom treated effectively: the need to face up the threat of intimidation by bigger kids and the discovery that notorious reputations are often grossly exaggerated. Seeing these experiences reflected more or less accurately may give the film -- opening today at area theaters -- a special claim on the affections of younger moviegoers.

As the pivotal character, a runty but resourceful high school sophomore named Clifford Peache (a handle that only adds to his problems), Chris Makepeace confirms the pleasant, smart impression he made last summer in "Meatballs." Clifford lives at Chicago's Ambassador East Hotel, where his father, played by Martin Mull, happens to be manager. After attending private schools exclusively, Clifford has decided to transfer to public school and the story begins on opening day.

The high school is no blackboard jungle; it's envisioned as a fairly respectable big-city institution whose student body includes a "bad" semi-tough element. The leader of the undesirables is called Melvin Moody, played by Matt Dillon -- a lean young actor who radiates amusing bad-boy vibrations, suggesting a teen-age edition of the early Richard Widmark. (He was seen earlier this year as Kristy McNichol's summer-camp sex partner in "Little Darlings.") A smug punk who obviously overrates himself. Moody operates an extortion racket in which vulnerable kids are bullied into paying a dollar a day for "protection," supposedly from the real brutes on campus, notable a brooding hulk of a boy named Rick Linderman, who is alleged to have committed rape and murder.

New student Clifford naturally qualifies as a mark for Moody. He becomes a more prominent target when he exposes Moody to ridicule in a class, and then to disciplinary action by school authorities. The latter results when the hotel chauffeur who has driven Clifford to and from school tells his father that Clifford was chased into the safety of the limo by Moody and his gang.

Mr. Peache calls the school, although Clifford hasn't said a word about day's tribution. Makepeace, blessed with a resonant, precociously expressive voice and a wonderfully sensitive face, is particularly adept at communicating the mixture of fear and shame Clifford feels at the prospect of being at Moody's mercy on the one hand and being sheltered by well-meaning grown-ups on the other.

Determined to find his own solution to the problem, Clifford takes an approach inspired partly by desperation and partly by keen observation. Perceiving that Moody and his cronies give a wide berth to the terrifying Linderman, Clifford boldly introduces himself to this menace and makes him an offer: a dollar a day for protection against the protection racketeers.

Initially rebuffed, Clifford persists, and something about his humorous persistence awakens a sympathetic response in the solitary, forbidding Linderman. Without compensation, the big kid is persuaded to back up the little kids, who relish the opportunity to defy Moody's authority one afternoon and finally get away with it.

Following this schoolyard liberation, the story appears to be pointed in an interesting new direction. One expects the filmmakers to concentrate on the evolving friendship between Clifford and Linderman, who have made common cause against the Moody faction but are still separated by temperament, grade, social class and experience. Linderman's personality is clouded by experience of a particularly tragic kind. Indeed, it's a distorted popular view of this experience that accounts for his notorious reputation.

The movie's principle artistic failing is that Ormsby seems to shy away from the friendship -- the strongest aspect of the story -- soon after discovering it. Instead of plunging deeper into the characters and family backgrounds of the boys, Ormsby is content to scratch the surface.

He could afford to do much more, especially with performers as appealing as Makepeace and Alan Baldwin, the 18-year-old newcomer cast as Linderman. They present an amusing physical contrast and develop excellent rapport. Baldwin makes Linderman a formidably attractive young hulk. He bears a resemblance to both Tony Bill and Warren Beatty but seems bigger, brawnier and more self-possessed. Baldwin can act, but he wouldn't necessarily have to in order to dominate a scene.

Clifford's domestic situation is trivialized by treating it as an excuse for comic relief with Ruth Gordon, cast as his irrepressible paternal grandmother. The identity and whereabouts of Clifford's remain a curious mystery, but Granny is all too present, accosting hotel guests with an eccentric familiarity that supposedly threatens her son's job. At this stage of her career it would be a startling reversal for Ruth Gordon to appear as an old lady who wasn't lewd or batty.

Linderman's family is slighted rather than trivialized. One lacks the first-hand documentation that might enrich the character's background and reinforce the emotional impact.

The success of "My Bodyguard" may depend on how willing audiences are to forgive its shortsighted superficiality. Everthing considered, it's worth making allowances. The film looms as a serious letdown only if one anticipates a big deal. The presence of promising new faces is always a good reason to give a movie the benefit of the doubt, and "My Bodyguard" is an attractive showcase for several.

Their good showing must owe a lot to the apparent generosity and confidence of Tony Bill behind the camera. Regarded as one of the more intelligent and reliable producers in the business, Bill is likely to follow the example of Alan J. Pakula and emerge as a capable, respectable director.

The movie feels intimate while looking relaxed ans spacious. The principal characters come alive with no apparent strain and seem to belong to the setting in which they're established. Bill doesn't get in the way of the subject matter or overdramatize a setting, as Alan Parker did in "Fame." t

Bill offers a decent dramatic premise the courtesy of a coherent, sympathetic interpretation. As techniques go, it's the next best thing to creative genius, and far more trustworthy.