Cutting Teeth

“Hey, I am naked for you,’’ Kellan Lutz said with the same smoldering expression that stares out from those Calvin Klein underwear ads of his.

OK, not really. Lutz wasn’t technically naked, just shirtless. But, as anyone who’s seen those ads knows, that’s plenty enough. And, truth be told, he was more nonchalant than anything. Caught bare-chested while changing clothes between appointments — and yes those were CK boxers peaking out from his low-slung navy slacks — Lutz looked like a young man who’s used to having people look at his abs.

But he was sweetly goofy about his physical perfection, too. “Ta da! I’m so pale,’’ he said at another point, lifting his white polo shirt upon request and slapping his six-pack. Then he mentioned his mom and how much he loves to eat and how he’s so lucky the vampires don’t go shirtless like the werewolves do.

The vampires would be the Cullen clan of the wildly popular “Twilight’’ franchise, whose third and latest installment opens Wednesday. Lutz plays Emmett, one of the lesser vampires in “The Twilight Saga: Eclipse,’’ a Cullen brother/bloodsucker to be sure, but one with few lines and nothing close to the screen time of pasty-white star Robert Pattinson. In the movie, Lutz is mostly used as muscle. He hulks around a lot.

Still, “Twilight’’ has changed his life, and certainly his acting options. It has for many of the young actors associated with the films. The white-hot light of celebrity doesn’t shine much brighter than it has on them, with their every move now chronicled and caught on cellphone cameras.

Lutz says he welcomes the attention, for the most part (a publicist cautioned “no personal questions’’ when he was asked about the actress with the equally flat stomach he is allegedly dating). There’s none of Pattinson’s moodiness, or Kristen Stewart’s crankiness, from him. He says he doesn’t even mind the changes he’s had to make to his old routine. (Those would include no longer jogging in his Speedo, the 6-foot-1 former swimmer said.)

“I’ve been very fortunate in that I’ve been acting for numerous years and doing other projects before ‘Twilight’ came,’’ Lutz said. “I think it would be different for someone who hasn’t been acting, going from zero to hero. It’s hard to maintain oneself when you have the world at your feet saying how great you are.

“Thank God,’’ he added, “we’re all at the age where we know who we are.’’

Lutz is 25. Much of the cast is early- to mid-20s, with the obvious exception of those who play the parents in the movie (vampire and human), as well as Stewart, 20, and 18-year-old Taylor Lautner, the good-guy werewolf whose wardrobe consists mainly of his smooth chest and butt-hugging shorts. Until the first “Twilight’’ in 2008, none of them was a star and, some movie and TV work aside, most were unknown.

Michael Welch, who plays an absolutely normal high-school student named Mike Newton — no fangs, no extra body hair — is 22 with a long acting resume that dates back to when he was in elementary school. His first role was as a young Niles on the “Frasier’’ TV show in 1998. But “Twilight’’ has been something else altogether, even for a character as minor as his.

“I do get some of that, certainly not to the degree of the big three stars of the film, which is fine by me,’’ Welch said of weepy, shrieking female fans. “One thing that keeps me grounded, I know that it’s the franchise and it’s not me. I’m just a lucky guy who got to be part of this journey. . .

“I know that when you are thrust into fame without having a foundation that you’ve built over the years, it can become very difficult to sustain that,’’ he added. “I don’t doubt I can make the transition into other work and I hope the same for all of my castmates and I wish them well, but probably some of them are going to have a hard time of it.’’

For now, however, the saga goes on. And on. Summit Entertainment is splitting the final novel in author Stephenie Meyer’s series into two installments, with the story slated to come to a close in 2012.

Director David Slade (“Hard Candy’’) inherited most of his “Eclipse’’ cast, although a villainous new vampire (Aussie actor Xavier Samuel) was his call. He jokes about them appearing at “Twilight’’ conventions years from now (“Come and sit on Batman’s lap. Is that your mom?’’) but stresses that he has no concerns that any of them will implode or be unable to make a living acting, if they want.

“What advice would I give these kids? It’s impossible to give them advice,’’ Slade said. “They’re all down to earth. They’re all hard-working, without exception, and I think that will do them fine. The main thing is that all these actors . . . know their craft and if they’re early in their careers, they’re well on their way to learning it.

“I don’t think,’’ he added, “that you’ll fill up your gas in 10 years and find one of them. They’ll all be just fine.’’

For his part, Lutz describes himself as a man with a plan. Vampiric victories and his stint opposite Lisa Kudrow on HBO’s “The Comeback’’ aside, his true aim is to be an action star. Sure there have been horror flicks (the remake of “A Nightmare on Elm Street’’ earlier this year) and there are romantic comedies coming (“Love, Wedding, Marriage’’). But what gets him going — and gets him to lift up his shirt again — is his role as Poseidon in next year’s “Immortals,’’ where he gets to play gladiator in the digital age. And he bears the (albeit small) scars of that shoot, literally, where he was sliced with a machete.

“I don’t have tattoos, but I wear these scars as tattoos,’’ he said, almost giddily. “I just love them. And that movie was my dream role. I did so much fighting in it.’’

Unlike his recurring character on the CW spinoff series “90210,’’ Lutz comes off less like arrogant athlete George Evans and more like an oversize everyman. He’s huge but huggy. He seems perfectly happy to be sitting in a swank hotel room talking about the franchise yet again — and uses the opportunity to highlight his pet projects: Royal Family Kids’ Camps for abused and abandoned children, and the St. Bernard Project, helping to rebuild housing post-Katrina. He can also be a bit geeky, and once considered becoming a chemical engineer. He still invents things and holds two patents.

“I really don’t care about fame,’’ Lutz said, diving into a plate of cookies. “Being a middle man in this franchise, it’s a blessing. Yeah, I’d enjoy being in Rob’s shoes or Taylor’s shoes, but it’s even better to benefit from it under the radar.’’

Lutz agrees with Welch, who says the entire cast shares a self-mocking camaraderie that makes any level of celebrity easier.

“We talk about the ridiculousness of the whole thing from our perspective,’’ Welch said. “I’m not saying it’s ridiculous but, yes, we know we’re not that big of a deal but other people think we are.’’ Boston Globe