For his latest feat, Oscar winning screen legend Robert De Niro plays two roles, as rival Mafia leaders Frank Costello and Vito Genovese at the mob’s late 1950s peak.

Another word for “feat” might be “stunt” or “gimmick” in the case of “The Alto Knights.” But what’s the movie rule for “gimmicks?” How good would the picture be without them?

Oscar winner Barry Levinson (“Rain Man”) and “Casino/Goodfellas” screenwriter Nicholas Pileggi cook up a pretty good mob history lesson to immerse the Two De Niros in. The gimmick doesn’t make the picture, but it does add to something to it, as DeNiro makes these two characters as distinct as young Vito Corleone from “The Godfather Part 2” and Paul Vitti from “Analyze This” and “That.”

In the 1950s, America was still living under the illusion that “The Mafia,” aka “La Cosa Nostra” aka “organized crime” didn’t exist. The apparently-closeted FBI chief for life J. Edgar Hoover sold that lie as part of his self-mythologizing. “No such thing as ‘organized’ crime.'” “The Alto Knights” is about the nation waking up from that stupor of corruption and realizing that the West Coast mob, the Northeastern Mob, the Chicago mob and the Miami mob, and all the big Italian-led mobs in between, were indeed “organized.”

Frank Costello was the mafia don above the dons, an ex-con and criminal figure who’d bought and bribed his way into charitable respectability and New York politics. He passed himself off as a modest Everyman who “takes taxis” lives well but not at all lavishly.

His childhood running mate Vito Genovese was an impulsive, never-polished goon who grew up with Costello in The Alto Knights Social Club in Hell’s Kitchen, New York. Vito’s efforts to manipulate the press and the “system” are more obvious and often ridiculed.

The movie’s about how Genovese tried to kill Costello, and the ripple effects of that which exposed the mafia and brought a reckoning for the “families” and the pugnatious mugs who ran them.

Even if you don’t know mafia history, and you could be a little lost in this if you are, a lot of the surnames will register in the memory — Gigante, Genovese, Anastasia, Bonanno, Lucchese, Costello and Gambino among them.

Pileggi’s script, voice-over narrated to death by De Niro as Costello, details the chain of events that connected “professional gambler,” “racketeer” and “Prime Minister of the Underworld” Costello to still-trigger-happy Genovese, whose idol had been Lucky Luciano, back in the day.

And through their feud, the career-making Kefauver Mafia Hearings in Congress and an infamous mob summit in Apalachin, New York, America and the world learned of the wide reach of the mafia and started to do something about it.

The story opens with an assassination attempt, which Costello survives.

“I got the message. That’s it. I’m done…I don’t wanna get killed over something I don’t want no more.”

He won’t speak of revenge, won’t endorse hotheaded underlings like Albert Anastasia (Michael Rispoli, very good) who want Vito “taken care of.”

But how can he manage that, with Genovese berating underlings who didn’t “finish the job” in ranting English and Italian complaints.

“The Alto Knights” is an old man’s movie, featuring old comrades and rivals, fat and rich and if not “happy,” at least carried to and fro in thebiggest, most luxurious American made sedans of the era. Even the state trooper who tracks them to their “commission” meeting is long in the tooth.

Genovese’s ex (Katherine Narducci) drags him to court. She drags Frank and his wife’s (Debra Messing) names into the public record.

Mobsters will die and Costello’s canny exit strategy is matched against Genovese’s terminal paranoia.

De Niro’s Costello is every inch the mob kingpin in winter, and exactly as you’d expect him to play the man — reserved, meditative and maybe even cunning. But his Genovese, in omnipresent hat and sporting a prosthetic chin, is one of his great creations — loathesome, simple and instinctual, a murderer who gets others to do his murdering for him these days.

Levinson and De Niro find humor in that lethal paranoia, and in how small a gang of gray-haired (mostly), pot-bellied (generally) underworld kings look when they’re cornered, out of their element, their Caddys, Lincolns and Imperials stuck in the Upstate New York mud.

The film needed more flashbacks to justify that “Alto Knights” of their youth title. And old pro Levinson knows voice-over narration is the lazy filmmaker’s creakiest crutch.

But De Niro’s the reason to see this, and whatever the De Niro Derangement Syndrome crowd may say, he carries “Alto Nights” as high as it goes. It’s not on a par with Scorsese or Coppola’s best statements on this history, but it’s not bad. And twice the De Niro at the same price makes it a bargain.

Rating: R, graphic violence, profanity

Cast: Robert DeNiro, Debra Messing, Kathrine Narducci, Michael Rispoli and Cosmo Jarvis

Credits: Directed by Barry Levinson, scripted by Nicholas Pileggi. A Warner Bros. release.

Running time: 2:00