In this bizarrely cheery adaptation of the Academy Award-winning film, suicide among young gay people proves difficult to sing about.There is no lack of cheese, God knows, in musicals. Worthiness is also plentiful — and sometimes more off-putting.Still, until “Trevor” opened on Wednesday at Stage 42, I’d seldom encountered, outside of after-school specials, the cheesy-but-worthy combo, a seemingly impossible platter that’s almost as righteous in the world as it is wrong in the theater.The righteousness of “Trevor” comes from its pedigree and its mission. Based on a 23-minute film of the same name, which won an Academy Award in 1995, it’s about a 13-year-old boy who can see only one solution — suicide — to the problem of being gay in a homophobic society. Told mostly in the form of voice-over diary entries, the film ably captures the desperate interiority of Trevor’s crisis, and the difficulty of relieving it with hope.Combating such hopelessness became part of the mission of the Trevor Project, founded in 1998 by the movie’s principal creators, including its screenwriter, James Lecesne, now known as Celeste. Through its 24-hour Trevor Lifeline and other services, the nonprofit aims to interrupt the cycle of hatred and self-hatred that can sometimes lead young people struggling with similar problems to dire acts.Though the organization and the musical are not affiliated, they do share the same name and the same source: a young gay character in Lecesne’s one-person show “Word of Mouth.” Less profitably, the musical also inherits the organization’s weighty responsibility in seeking to address despair without modeling it. However foundational it may be as a medical precept, “First, do no harm” is disastrous as a musical one.The result is a bizarrely cheery and thus tonally incomprehensible show in which everything potentially painful is anesthetized by saccharine songs and middle school clichés. When the very bright lights (by Peter Kaczorowski) rise on Donyale Werle’s Lakeview Junior High set, with its colorful linoleum, neat banks of lockers and prominent trophy case, you may feel you are in for an ordinary pubescent comedy along the lines of “Mean Girls.” Nothing suggests that Trevor (Holden William Hagelberger) will have anything worse to face in the course of the action than the general failure of the world to recognize his fabulousness.That fabulousness is a pileup of gay markers: Trevor is obsessed with Broadway, dance and, above all, Diana Ross, who appears in a series of fantasy sequences (and spangly outfits by Mara Blumenfeld) to encourage the boy on his journey of self-acceptance. Exactly what he has to accept is apparently hard to say, as the word “gay” occurs only once in the script, three-quarters of the way through. Even then, it’s oddly disowned and unidiomatic: “Everyone at school is saying that I’m a gay,” Trevor tells us, doubtfully.Setting the show in 1981 may be meant in part to excuse this “love that dare not speak its name” — or even think it — mentality. Even so, cloaking Trevor’s truth in euphemisms like “weird” and “artistic” decouples his self-discovery from the violence of his classmates’ response, and his own. It’s not because he’s “creative” that they turn on him or that he eventually turns on himself.Gotta dance: Hagelberger, right, with cast members in “Trevor.”Sara Krulwich/The New York TimesThis central obfuscation leaves you wondering, for most of the musical, whether something will ever happen worth singing about. There are only so many “I want” numbers and charm songs — two of the templates in the musical theater handbook — a show can support before a crisis had better step forward.Yet despite disengaged, Reagan-obsessed parents at home and goony boys and boy-crazy girls at school, Trevor is presented as basically happy in his life with the imaginary Ross (Yasmeen Sulieman) and his circle of genuine outcasts. Walter (Aryan Simhadri) may show him the wrong kind of porn (women wearing lingerie on a farm), and Cathy (Alyssa Emily Marvin) may misunderstand his intentions (she can’t wait to kiss him despite her braces), but they tolerate his idiosyncrasies. Cathy has “watched every Tony Awards with him since 1976.”Even the school’s dim heartthrob, a jock named Pinky (Sammy Dell), befriends him, encouraging Trevor to choreograph a Tommy Tune-like dance routine for the football team at the annual talent show. (The choreography by Josh Prince charts a careful middle course between unappealingly clumsy and unbelievably slick.) And though the first act ends with the implosion of this spectacle — the team performs a different routine instead — the stakes feel dangerously low until it’s almost too late to revive them.What went so wrong? In the first place, turning this material into a musical may not have been wise. Unlike naturalistic movies or prose fiction, musicals disperse the point of view to anyone who sings. Tonal subtleties delivered through Trevor’s eyes in the film cannot be contained that way onstage, and so a lot of the charming naïveté of the original becomes vague and clammy in Dan Collins’s book.The songs, with lyrics by Collins and music by Julianne Wick Davis, don’t do much better; though professional, they are mostly upbeat and synthetic regardless of the moment, marking time instead of making points. They also face an unfair fight against the Ross catalog, including excerpts from hits like “Ain’t No Mountain High Enough,” “Upside Down,” “It’s My Turn,” “Endless Love” and, inevitably, “I’m Coming Out.”The exceptions to the score’s blandness are telling. A number in which Pinky teaches Trevor to play H-O-R-S-E in gym class — including the double-edged instruction “you don’t want to spell it out” — is characterful, specific and sweet. “One of These Days” has Trevor returning the favor, teaching Pinky to imagine what he might be like in 10 years. Later the song returns, poignantly, after Trevor swallows “way too many aspirin” and winds up in the hospital.It is only in such moments, when the musical acknowledges its givens, that it comes to life. The scene between Trevor and a candy striper, apparently gay himself but old enough to have passed through the tunnel of adolescence, is as frankly and thoughtfully written as you wish everything else were.Is it a surprise, then, that for the first time in the show, the performances, under Marc Bruni’s otherwise hectic and skin-deep direction, strike real notes and admit real feeling? Hagelberger, 13, finally seems 13, not 9, and Aaron Alcaraz, as the candy striper, achieves in two minutes what the rest of the show fails to in more than two hours: musical comedy lightness anchored in honest emotion.Hagelberger and Aaron Alcarez.Sara Krulwich/The New York TimesIt’s not that the message of that hospital scene is so novel; it’s basically an It Gets Better ad, deftly dramatized. In less deft moments the musical feels as if it were written for, or even by, suicide prevention experts worried about copycatting.I understand the concern, but then why write a musical? You can’t keep saying that a show is not about what it’s obviously about. And yet, as I imagine “Trevor” being performed for young audiences, perhaps in middle schools that even today are scenes of vicious homophobia, I have to think the ends justify the means. In the level of heaven reserved for works of the imagination that have saved real lives, “Trevor,” in 10 years, may be holding court on a special and I hope very fabulous cloud.TrevorAt Stage 42, Manhattan; 212-239-6200, trevorthemusical.com. Running time: 2 hours 15 minutes. More