One of the people who’s made long-form television drama arguably more interesting as a whole than its mainstream big-screen equivalent in recent years, Alan Ball has underlined his superior comfort with that format in the few theatrical features he’s made to date. His screenplay for “American Beauty,” which Sam Mendes directed, was brilliant but glib; as writer-director of 2007’s “Towelhead,” he couldn’t quite make the complicated agenda of Alicia Erian’s novel gel in two-hour form.

His first such enterprise since, the somewhat autobiographically inspired “Uncle Frank,” hits a more successful balance between ensemble seriocomedy, Big Issues and a somewhat pressure-cooked plot. Set in the early ’70s, it casts the reliably deft Paul Bettany as a gay man forced to confront the Southern family to whom he’s stayed closeted — though they’ve managed to communicate tacit disapproval of his being “different” anyhow. Well-cast and gracefully handled, this is a nuanced plea for loving acceptance that should appeal to a fairly broad audience, even if it does lay on the tearful melodramatics pretty thick in the last lap.

As a 14-year-old in small-town South Carolina, precocious Carson McCullers-in-training type Beth Bleshoe (Sophia Lillis) feels pretty different herself, fitting in with neither her rambunctious family’s hyperactive grade-school kids nor its snippy high school girls. Grandpa (Stephen Root) is a heavy-handed patriarch her father (Steve Zahn) tries to emulate, while the womenfolk (including Judy Greer and Margo Martindale as Beth’s mother and grandma, respectively) stick to fussing in the kitchen.

The only person Beth really enjoys being around, and who actually listens to what she has to say, is her infrequently visiting Uncle Frank (Bettany), a literature professor who fled to NYC a long time ago. Yet despite his being “smart and funny and considerate,” Beth can’t help noticing how he’s subtly excluded by much of the family — or not so subtly, in Grandpa’s case. When Frank encourages her to think outside the small-minded local box and create her own identity, she takes those words to heart. Thus four years later, she’s a university freshman at NYU, where he teaches.

Thanks to the conniving of a more sophisticated classmate (Colton Ryan), Beth soon discovers Frank’s secret — not only is he not married to a previously introduced beard “wife” (Britt Rentschler as a lesbian flatmate), but he’s been living with boyfriend Walid, aka Wally (Peter Macdissi), for a decade. This news has barely been digested when the runaway Bledsoes are called back to the Carolinas. There’s been a death, and all must pay their respects, reluctantly or not.

The drive down gets more complicated when it’s discovered that Wally has been tailing Frank and niece. In one of the weaker plot points here, he simply can’t understand why he can’t be introduced to his lover’s family — even though in the Saudi culture he left behind, such acknowledgment of homosexuality might be greeted by arrest and execution.

Attractively produced, with nice period design details and handsome lensing by Khalid Mohtaseb, “Uncle Frank” recalls plenty of prior coming-out (and coming-of-age) sagas, but revisits their familiar terrain with a confident and skilled mix of humor and character-dynamic shorthand.

Occasional on-the-nose moments grow more frequent on the road south, as Frank has gauzy flashbacks to a doomed teenage romance (enacted by Cole Doman and Michael Perez), then upon arrival, as he falls off the wagon even before funeral-related events take a humiliatingly cruel turn. With tragedy in the past and present, accompanied by many tears, arguments, hugs and healing affirmations, the movie piles on more histrionic display than necessary to reach the inevitable blended-new-family-of-the-future fadeout.

Those late excesses will work just fine for many viewers, however, and even at its most manipulative, “Uncle Frank” remains polished and engaging. A big plus is Bettany, who makes the title character’s residual Southern courtliness, acquired urbanity and painful psychological scars keenly felt. Though Beth is something of a stock audience stand-in device, Lillis is thoroughly convincing as a youth of her era and background, something that one can no longer count on these days.