Watch ‘Rita Moreno: Just a Girl Who Decided to Go for It’: Still Going at 89

Rita Moreno’s most indelible screen moment, which had her and a “West Side Story” ensemble sizing up the pros and cons of their adopted U.S. homeland, remains an eternally clever musical argument over whether “America” is a dream or nightmare for immigrants, settling in at a 50/50 split. The balance is skewed more along the lines of 80/20, in favor of dream, for the star herself in “Rita Moreno: Just a Girl Who Decided to Go for It.” Premiering at Sundance, the documentary from the theatrical wing of “American Masters” cheerfully jumps from one heartening career reinvention to the next, with sobering lulls to ponder what an even more prolific filmography she might have had without profligate racism and sexism standing in her path.

The list of executive producers includes longtime pal and partner-in-social-consciousness Norman Lear, as well as the man who’s followed in Moreno’s footsteps as the leading American exemplar of Puerto Rican pride, Lin-Manuel Miranda. That doesn’t augur well for a warts-and-all approach. but the repeated explosions of uplift in director Mariem Pérez Riera’s doc feel pretty well-earned. It’s hard to think of many screen sirens still around from the studio system’s last golden age who have not only lived to tell the tale, at 89 (as of the film’s premiere), but are still doing acclaimed work and are activist enough to have “role model” permanently etched into their résumés.

The setup has Moreno planning her own festive birthday party, as is apparently her wont, with a jaunty jazz score that suggests we’re about to see a feature-length enshrinement of a Grande Olde Dame. The star looks impossibly glamorous for her principal interview. Soon enough, we do see footage of Moreno before she cleans up so good, as she arrives on the “One Day at a Time” set on the Sony lot — echoing her early days as an MGM starlet — to do her own makeup.

In or out of glam mode, though, it’s clear that Moreno is just about always “on,” and as far as we can see, that’s a good thing. “I may be petite, but I’m big,” she says late in the film, talking about her long marriage to a husband who wished she would tamp down her outsize personality. Her thoughtfulness notwithstanding, Moreno makes no bones about it: She lives to be vivaciously entertaining, on- and off-screen.

There’s not much evidence here that Moreno has a dark side, which makes it especially bracing when she does suddenly switch out of charm mode to frankly and unflinchingly address the more sinister sides of Hollywood she encountered on her way up as “a Spanish Elizabeth Taylor.” She describes early would-be mentor Harry Cohn as “a distinctly vulgar and crude man” who thought “You know I’d like to f— you” was a workable come-on. Years later, when she’d made a name for herself, Moreno’s agent raped her, she says, and “I still let him be my agent, because he was the only one that was helping me in my so-called career.”

These harrowing but not atypical moments of misogyny give way to some unique problems Moreno faced as the face of Latinas on the big screen for quite some time. She was put into a succession of “island girl” roles, often wearing “makeup the color of mud,” even after she got a choice non-“ethnic” role in “Singin’ in the Rain.” For her career-making turn in “West Side Story,” she appeared in an embarrassing brown-face that mars one of the otherwise great musicals of all time.

But after a mysterious career drought after winning the supporting actress Oscar for that performance, Moreno came back and conquered the EGOT mountain with projects as disparate as night and day — her performances in Broadway’s (and the movies’) bathhouse-set “The Ritz,” and in TV’s kids’ series “The Electric Company.” Those twin comebacks seem like they’ve established her breadth once and for all, till the doc gets to her run as the mousy-looking but stoically fierce nun-shrink in “Oz,” where Moreno forever proved that she could get small, too.

You keep wishing the clips were longer; who wouldn’t want an hour and a half just of “Electric Company” scenes with Moreno playing against Morgan Freeman (who shows up as one of the talking heads here)? Some personal-life elements seem even more breezed over: In the early narrative, there’s little follow-up on the provocative question of whether she was traumatized when she and her mother left the rest of the family behind to come to the U.S. from Puerto Rico. An early ‘60s suicide attempt comes up and basically goes unexplored. Her 7-or-8-year relationship with Marlon Brando feels like it deserves its own movie, although maybe the fight scene from their co-starring stint in “The Night of the Following Day” says nearly enough.

But the pride that infuses the movie — the admiration that comes from her costars, and the admiration of her Latinx acolytes and mentees, as well as her own self-belief — comes at just the right length. Not many potential subjects for docs of this sort really justify being put in a character arc that involves so many micro-rises and falls before such an extended and graceful plateau. Coming away from “Just a Girl,” it’s impossible not to be convinced that Moreno is the rare screen legend who found a way to stick the Hollywood landing.