"The moment you don't do that, give it up," Stewart told reporters in New York recently.
"'X-Men' is as important, as serious a piece of work as Strindberg or Ibsen. You don't short-change the work because it happens to be a comic-book franchise for a studio. I think entertainment is a really serious business. I don't mean that it can't be funny and entertaining, but I think that entertaining should be taken seriously and not lightly, half-heartedly, so there is no difference at all, it's just that your energies get directed in somewhat different ways in the theatre or television or film."
A respected stage actor, Stewart is perhaps best-known to Americans as Capt. Jean-Luc Picard from the "Star Trek: The Next Generation" television show and movies, and Professor Charles Xavier from the 2000 blockbuster "X-Men," based on the classic Stan Lee comic-book series.
The 62-year-old Brit took time out from rehearsing for the upcoming West End production of Ibsen's "The Master Builder" to promote the "X2: X-Men United," due out Friday.
Asked to compare stage and film acting, Stewart said the main distinction between the two disciplines was the time one had to invest in memorizing his lines.
"I became an actor to work on stage," he explained. "I didn't become an actor to spend time in front of a camera or sitting in my trailer. Not that I have anything against movies at all you understand; on the contrary. But the play that I'm rehearsing in the script version that I've got is 129 pages and I am on 121 of them and I talk most of the time... Right now in my learning process I'm around about page 75. Some time in the next 10 days, a moment will come, I know it will come, when I can say, 'I know it! I know it! I can do a run-through off the book.' Right now, that is the one major difference because with movies... An American actor once said, 'Give my lines and a comb.' (Stewart pretends he is reading his lines and combing his hair.) 'Yeah. Yeah. Yeah. Yeah. Let's shoot it.'"
Stewart isn't the only "X-Men" alum performing in the West End this spring. Ian McKellen, who plays bad guy Magneto in the films, is doing August Strindberg's "Dance of Death."
"I went to see him last week in his play," Stewart noted. "He's terrific in it. It was delightful to come out and find that there were a big bunch of fans who had in one hand the program for 'Dance of Death' and in the other pictures of Gandalf (McKellen's character in 'Lord of the Rings') or Magneto."
Although he plays the quintessential leader in his "Star Trek" and "X-Men" films, Stewart insisted that he never tries to be a father figure on a film or television set. Told that director Bryan Singer described him as such in a recent interview, Stewart gasped, "He said that?"
"I refuse to become a father figure for Bryan Singer. I am too young and attractive," he declared.
So, was McKellen the one to shepherd younger cast members?
"No!" he exclaimed. "Certainly not! No way is he going to become a father figure for anybody. Hugh! Hugh Jackman. He's the guy that takes care of everybody, looks out for everybody. Not me. Absolutely not. I'm too much of a rebel. He was the good guy. If you've got problems, he'll (help you out.) He's actually the sweetest man in the world and really will take care of you. No, no, no. I think that Bryan has this idea that I am this all-powerful individual, but little by little, he's learning that's not the case."
From some of the reports that came from the "X-Men" set, it sounds like Jackman probably had his hands full. Stewart acknowledged that there was some tension during production, but he emphasized that Singer's infamous temper was balanced with his enthusiasm for the project, adding that the atmosphere on the set of the second film was much lighter than that it was on the first.
"It was different," he recalled. "It was much more relaxed, much more easy-going. Bryan yelled less, which was good, except the only down-side of that was that he kept telling people how less he was yelling."
Confirming that the script underwent several last-minute rewrites and the cast was forced to improvise some scenes to work out kinks in the story, Stewart said these weren't necessarily bad things.
"Don't look on that in a pejorative way," he remarked. "It was creativity and Bryan is a perfectionist and if he doesn't think either the script for that day's work is right or there's something wrong with someone's costume, he won't roll the camera. He's not going to just film something unless he's absolutely convinced it is what it should be... Bryan is, above all else, he is an enthusiast. The one way in which I contrast Bryan with almost any other director I know is that Bryan can't wait to show you what he just shot. He'll say: 'Come see! Come see! Look at this...You want to come, security guard? Everybody come see what we shot. I've got 15 minutes edited together.' It's so infectious that. In the meantime, the set waits while Bryan is showing this.... But how can you resist that kind of enthusiasm?
"I was very attracted to that," he added. "I love enthusiasm. It's one thing that separates the British from other people. We tend to look down on enthusiasm somewhat. It's not cool to be too enthusiastic."
Stewart can next be seen opposite Glenn Close in a Showtime production of "The Lion in Winter," which he executive produced with his wife.
Notable deaths of 2014 [PHOTOS]