The movie posters promise that “X-Men: First Class” will be released June 3, but on Tuesday cameras were still rolling on the Fox film’s set and director Matthew Vaughn, making his biggest major studio feature film to date, sounded like a man running out of time. “I’m at that stage where I feel like a boxer against the ropes,” the director said as his crew prepared for the next shot on a location set in Long Beach. “I’m just throwing punches and taking them as they come and making sure I don’t hit the canvas.”

In the pages of Marvel Comics, the X-Men have been the ultimate outsiders for decades — even other superheroes view the strange mutant crew with mistrust, prejudice and disdain. So it’s fitting that “First Class,” the fifth Hollywood adventure for the heroes, will arrive in theaters this summer with so much to prove and plenty of doubters. For the all-new cast (led by James McAvoy and Michael Fassbender), the challenge is to replace the familiar faces of the franchise; for producer Bryan Singer, the challenge is to recapture the affection of comic-book movie fans; and for Vaughn, the challenge is, well, to actually finish making the film.

“We’re filming at the moment, we’ve a lot to get done,” said a weary Vaughn, whose credits include memorable but modest-grossing indie fare like “Kick-Ass” and “Layer Cake.” “I’ve never worked under such time pressure. The good thing about the independent world is I never even knew if I was going to get distribution. I’m used to finishing a film and then crossing your fingers that someone is going to like it. This is totally doing it the other way around. We’ve definitely got a release date and we’ve got to make it.”

Vaughn is famous for firebrand candor and droll wit, and despite the hand-wringing right now among some Fox executives, the British filmmaker isn’t turning meek under the pressure. Asked if he’s concerned about the glut of superhero film competition this summer — with “Captain America: The First Avenger,” “Green Lantern” and  ”Thor” – Vaughn said that, if anything, it’s the other guys who should be nervous. “With ‘Green Lantern,’ I don’t know about that one, I couldn’t get my head around the trailer, to be honest … look, I will say the following: X-Men as a brand is bigger than Captain America, Thor and the Green Lantern, all put together.”

And that is the X factor that Fox is counting on. The four mutant-hero movies to date have pulled in $1.53 billion in worldwide box office, and even when the hard-core fans of the comics grumbled about the quality of some of the movies (as they did with the Brett Ratner’s 2006 installment “X-Men: The Last Stand”), many of them still bought their tickets just so they could join in the intense Internet debates. The opposite of love isn’t hate, it’s apathy — and to date there has been no apathy when it comes to the X-Men characters that created a publishing bonanza for Marvel in the 1980s and 1990s.

“First Class” is being described as an origin story by the studio, and it is set in the 1960s, the same decade that artist Jack Kirby and writer Stan Lee introduced the uncanny X-Men into the cosmic melodrama of their expanding Marvel universe. McAvoy is taking on the role of youngCharles Xavier, the leader of the X-Men, and Fassbender is Erik Lehnsherr, the man who will become the evil mastermind Magneto. McAvoy and Fassbender are taking over movie roles originated by Patrick Stewart and Ian McKellen, respectively, two esteemed actors who are practically revered among sci-fi and fantasy fans for their respective work in the ”Star Trek” and”The Lord of the Rings“  universes.

McAvoy has flipped between roles of art-house acclaim (“Atonement,” “The Last King of Scotland“)  and work in special-effects blockbusters (the first ”Chronicles of Narnia” film, “Wanted“) and he said that Stewart’s work as the aged, bald and wheelchair-bound Xavier is something he views as a counterpoint, not as competition.

James McAvoy and Michael Fassbender in "X-Men: First Class" (Fox)

“This isn’t a reboot, so I’m not replacing anyone, in which case you might want to try to be as different as possible and stay away from what had been done before,” McAvoy said on Monday during a break from a rescue scene that required water-tank work. “This is a prequel, so I’m the same character, just younger, but the challenge for me – and for Michael — is to show the same person in a different place in their life; to show someone before they’re this bad guy, before they’re this saint. Charles wasn’t always a … monk, this selfless, sexless monk that he becomes.”

The plot of this film is still under wraps, but it presents a world where superpowered mutants are living in secret and don’t face the public scrutiny and prejudice that are central themes in the earlier films, which are primarily set in the modern day. The friendship of future foes Xavier and Lehnsherr is the heart of the film — Singer says the two have a common cause and different approaches and he even used the life trajectories of the Rev. Martin Luther King Jr. andMalcolm X as a sort of shorthand for their veering paths. Despite rumors to the contrary, Vaughn said the movie will be the first X-Men film without the most famous face of the franchise,Hugh Jackman’s Wolverine, and key characters such as Cyclops, Storm and Jean Greygive way to new screen arrivals such as Emma Frost (January Jones), Azazel (Jason Flemyng), Sebastian Shaw (Kevin Bacon) and Havok (Lucas Till). 

“It is an excellent cast,” Singer said. He added that no one is more aware of the high-bar set by McKellen and Stewart. “I’m very sensitive to it. Michael Fassbender and James McAvoy are two of the best actors working today and that was needed to fill those shoes. Short of digitally recreating Patrick and Ian in their 20s I cant think of anyone who would be more equipped for this than these two guys. The challenge of that is what attracted James, I’m sure of it. That’s why the guy who starred in ‘Atonement’ would want to play a comic-book character in the first place because it was a role established by a really fine actor.”

Singer directed the first two “X-Men” films — which many observers cite as the starting point of more sophisticated treatment of superheroes in cinema — and then left the franchise to direct “Superman Returns,” a movie that was, on paper, a commercial success but culturally and artistically failed to capture lightning in a  bottle as the filmmaker had hoped. Now he’s returning as a producer for this “X-Men” installment and still hopes to direct another X-movie in the near future. He praised Vaughn’s vision and attention to detail and said the problems the production is now facing are merely intriguing challenges that will be overcome.

“The biggest challenge is introducing an audience to these characters in a different time – characters the audience is familiar with but now see played by younger actors and in a story taking place in a different time. We have to establish this universe. We had the challenge with the first ‘X-Men’ film, which came at a time when there were no comic-book movies [of this sort] and no template to launch from and yet you’ve got to do that. You have to put your characters out there and introduce them to a quizzical public that sort of recognizes them. But that very thing is the exciting part of it.”

– Geoff Boucher