It’s the story of a guy, a girl and the coolest city in the world. And, hard as it is to believe, it was released 50 years ago this month.

“Viva Las Vegas,” the 1964 musical directed by George Sidney and starring Ann-Margret and Elvis Presley, is considered by aficionados of Elvis’ cinematic oeuvre to be one of the best, if not the best, film he ever made.

“Viva Las Vegas” has it all. A kinetic, frenetic look at Las Vegas at its hippest. Ann-Margret, the only leading lady who ever could match Elvis’ charisma and smoldering sensuality on screen. A score that spawned a song that everybody knows, every band covers and nobody can get out of their heads once he hears it.

“Viva Las Vegas” is a great movie, and the story behind it is pretty good, too. On Saturday, Sean Clark, a screenwriter, producer and an associate film professor at the University of Nevada, Las Vegas, will talk about the quintessential Las Vegas film during a program at the Clark County Library, 1401 E. Flamingo Road.

The program, which begins at 2 p.m., will include a screening of “Viva Las Vegas.” It’s co-sponsored by UNLV’s film department and is free. For more information, call 702-507-3459 or visit www.lvccld.org.

Like most of Elvis Presley’s cinematic output, the plot of “Viva Las Vegas” is as flimsy as a showgirl’s feather: Race car driver Lucky Jackson hits town to compete in the Las Vegas Grand Prix. His engine goes bad. Needing bucks, he gets a job and meets part-time lifeguard/singer/dancer Rusty Martin. The adjectivally named couple flirt, fight, dance and sing before, of course, (spoiler alert) marrying.

But, as with every other movie musical Elvis acted in over the 14 years that he cranked these things out, the important thing isn’t the plot but, rather, how it all comes together. And, in “Viva Las Vegas,” it’s director George Sidney who so adroitly creates an iconic whole.

Sidney was an award-winning Hollywood veteran whose major-musical credits are so impressive — “Bye Bye Birdie,” “Pal Joey,” “Show Boat” “Annie Get Your Gun” and “Anchors Aweigh!” among them — you’d think the only reason he’d agree to direct a Presley movie is that he lost a bet.

For Elvis, Sidney was the perfect director at the perfect time. Before “Viva Las Vegas,” Elvis had acted in a mostly forgettable string of movies, most of them formulaic musicals, and by the time “Viva Las Vegas” started filming in Las Vegas in 1963, Presley’s cinematic star had fallen.

“We don’t realize it, but this is at a lull in his career, because (his) movies have not been successful and the bloom is off the rose,” Clark explains.

That, he continues, is why MGM “came to George, because he’s one of the most accomplished musical directors of the time.”

Sidney “was one of the big dogs,” Clark says. “So they came to him and said, ‘We want you to do this, George.’ ”

Sidney liked Las Vegas and visited here often, says Clark, who became friends with Sidney after the director’s retirement, when he moved here and began working regularly with UNLV film students (the college’s Nevada entertainer/artist hall of fame award is named the “Sidney,” after the director, who also was its first recipient).

Sidney “knew the days of the, quote, MGM musicals were gone,” Clark says, and he already had begun filming movies outside of Hollywood. And, Clark says, “George always loved a challenge.”

Corinne Sidney, George Sidney’s widow, recalls, too, that the director was very close friends with her first husband, Jack Entratter, and the Sands executive encouraged Sidney to make a movie that would show off Las Vegas.

“George loved Las Vegas,” she says, “and he said, ‘Why not?’ ”

Studio executives had told Sidney that the way to put Elvis’ cinematic career back on track would be to “pump up the production values,” Clark says. “He said: ‘No, you need to give him a leading woman.’  ”

Giving Elvis a strong leading lady would go against the template that had been established in the singer’s films up until then.

“His handlers were always, ‘You cast somebody sweet and forgettable who wouldn’t overshadow Elvis,’ ” Clark explains. “It was George who said, ‘Get Ann-Margret.’ ”

Ann-Margret recently had worked with Sidney in “Bye Bye Birdie” and the director knew she could give the film a dynamic, hip energy. Elvis’ camp had qualms, but Sidney stood behind his choice. When the falling fortunes of Elvis’ movies went head to head against Sidney’s talent and reputation, there was no contest.

“It was simple: They had gone to this formula, and it was just barely a notch above bad TV,” Clark says. “They were just serving his personality, and it was George who said, ‘Ann-Margret changes everything.’ ”

Paul Casey, a former Elvis impersonator and now Las Vegas show producer, agrees. Seeing a strong leading lady in an Elvis movie “was a rarity, because most female co-stars with Elvis were just pretty,” he says.

“Some of them in the beginning were serious actors — Carolyn Jones in ‘King Creole’ or Debra Paget in his first movie (‘Love Me Tender,’ 1956). The problem is that, after a while, they got to be cookie-cutter.”

Ann-Margret was different, Casey says. “When the two of them are on screen, there’s an energy there. I think it was because they had a mutual admiration and fondness for each other.”

Sidney’s acumen for sharp casting also extended to the rest of the movie’s cast. For example, William Demarest — boomers know him best as Uncle Charley from “My Three Sons” — was cast as Ann-Margret’s father.

Demarest “was always a great comic foil,” Clark says. “The interplay with Ann-Margret and her dad is very well-crafted.”

“Viva Las Vegas” takes full advantage of the lights and color of the Strip and the city’s resorts, but also shows off Hoover Dam, Lake Mead, Mount Charleston and other parts of the city. Clark says Sidney also tweaked the structure of the traditional movie musical for the film.

In a traditional musical, “the songs take over when there’s an overflow of powerful emotions,” Clark says. “So we can give to a song that which we will not (express) in dialogue.”

That’s not uniformly true in “Viva Las Vegas.” While a few songs do allow characters to express emotion, “in an odd way, in ‘Viva Las Vegas,’ some songs are there because they seem like a good place for a song,” Clark says.

Sidney, who liked to operate his own camera, also devised some creative ways to get what he needed. For instance, the studio balked at paying extras for the race scenes, Clark says, “so they basically said, ‘Want to be in a movie? Come and stand on the sidewalk,’ and then they drove the cars right through.”

And that song? Written by Doc Pomus and Mort Shuman, “Viva Las Vegas,” released as the B-side of “What’d I Say” from the film’s soundtrack, became a classic, covered by everybody from Bruce Springsteen to the Dead Kennedys.

“To this day, wherever you go, if you’re from Las Vegas, they start singing that to you,” Casey says.

The “Viva Las Vegas” movie was released on May 20, 1964, and was, depending on whose figures one uses, around the 14th top money-earner of 1964 worldwide. The buzz on its release was international, Clark says.

Elvis made 16 more musicals after “Viva Las Vegas,” but almost all of them reverted to forgettable pre-“Viva Las Vegas” form. None was directed by someone of Sidney’s talent or stature. None featured a leading lady as sexy or as talented as Ann-Margret. And none would become as fondly remembered as “Viva Las Vegas.”

“The great thing is, it showed the diversity of Elvis,” Casey says. “Not only did he have, I believe, star presence that was always there, but he could be on screen with somebody with equal charisma but a female (actress), and it wasn’t threatening to him or to the audience.”

Presley confidante Joe Esposito considers “Viva Las Vegas” to be one of the best films Elvis made, and says Presley agreed.

“It was definitely one of his favorite films,” Esposito says in a recent phone interview. Elvis and Ann-Margret “got along so good together. They just clicked, and they were great, and became very, very good friends after the movie was over.”

“(The movie) only works if it really clicks with the two of them together,” he adds. “If somebody else did ‘Viva Las Vegas,’ would it have made a difference? Well, we’ll never know that. But they clicked together. They were really good together.”

Why didn’t Elvis and his camp continue the winning formula Sidney had devised? “Because George was a sweet man who had a way of getting what he wanted, and the Elvis people liked the way they liked things done,” Clark says. “So we go back to ‘Clambake.’ ”

What did Sidney think of the film? Corinne Sidney recalls visiting the Department of Motor Vehicles to get license plates not long after she and her husband moved here.

While waiting, “I asked, ‘What are you going to put on yours?’ ” she says. “He said, ‘I don’t know.’ I said, ‘Why don’t you get, ‘Viva Las Vegas’? He said, ‘Oh, God, Corinne. It’s the worst movie I ever made.’

“So we get in, and I said I’ll just have a plain plate. He said to the woman, ‘I want V LAS V’ — he said ‘to let everyone know I did that horrible movie.’  ”

Clark recalls that Sidney’s phone messages often would include some variation of the phrase “Viva Las Vegas” because “he knew he had something popular with that alone. That phrase just falls off the lips. It’s the perfect title.”

George Sidney died May 5, 2002, but Corinne Sidney is reminded regularly how enduringly popular “Viva Las Vegas” is.

“I get a residual every month,” she says with a laugh. “I must get five dollars every month. And, I get fan letters to George.”