BLOGGERS breathlessly describe his “porn-cut torso” and “delicious face,” and fans bring binoculars when he’s on stage.

It wouldn’t be surprising if Nathan Gunn were an actor or rapper – but an opera singer?

Ah, yes. In the world of Macy’s Thanksgiving Day parade-size divas and tubby, hanky-clutching tenors, the 35-year-old baritone is a gorgeous anomaly.

Not only can he sing, act and, if need be, scale a ladder, climb rigging or jump on a table (often with his shirt off), but – spoiler alert – he’s a happily married, Midwestern father of five.

After performing at opera houses around the world (and in auditoriums with his mother-in-law’s high-school chorus), Gunn is positively smoking as the bare-chested star of “An American Tragedy,” which bowed last week at the Met.

Critics otherwise left cold by Tobias Picker’s opera warmed to its cast, especially Gunn’s social-climbing serial seducer, Clyde Griffiths, who knocks off his pregnant sweetie to get ahead.

Those who know him say that is so not Nathan.

“We’ve been friends for a long time and working with him is, well, heaven,” says mezzo-soprano Susan Graham, who, as Gunn’s upper-crust girlfriend, Sondra, enjoys a few steamy, onstage kisses.

“He’s naturally gifted, but I also have enormous respect for him as a person – he’s so young, he has five kids and a wife who’s his musical collaborator, and he’s devoted to them.

“Do you realize how rare that is?”

Julie Jordan Gunn, the pianist who met and married the singer while they were students at the University of Illinois, takes the fuss in stride.

“I know about those blogs, but I don’t read them,” she tells The Post.

“It’s a good thing, I think, for him – and it’s good that opera has people who excite that kind of response.”

Yes, she concedes, “He has to take off his shirt a lot, but I think he wants to sing well enough to make that not cheesy. You don’t want to be known for your pectoral muscles!”

Over coffee the other day, Gunn – wearing severe-looking glasses (“My 10-year-old daughter picked them out”) – talked about beefcake and opera, and where he draws the line.

For a production of Britten’s “Billy Budd” in Munich last year, he says, the director had wanted him on stage dead and “totally naked,” then be carried off by his co-star.

“Gee,” Gunn demurred. “That sounds kind of cheap.”

The singer who had to carry him was even more insistent: “There’s no way I’m going to carry him over my shoulder with his bare butt in my face!”

Gunn got to keep his clothes on.

Still, he says in a warm, smooth voice some have compared to Bing Crosby’s, there are times nudity might be appropriate – say, in a love scene from “La Traviata” or “Romeo and Juliet.” (FYI to those Googling for shots of a Naked Gunn: There aren’t any, he says.)

“The funny thing is, I’m really kind of a reluctant artist,” he says. “I was a very shy kid growing up. I wouldn’t even ask the teacher to go to the bathroom because it was too embarrassing.”

Back in South Bend, Ind., he studied martial arts (and has two black belts to show for it) and listened to Pink Floyd, Metallica and Prince. As “the little boy with the good voice,” he was always tapped for shows and choirs, but didn’t take voice lessons until high school.

That’s when he got his first earful of opera, via Mozart’s “The Magic Flute.” Suddenly, he knew what he wanted to do.

“It’s all quality,” he insists. “The music, the words and the drama. The fact that it’s live makes it real. There’s no barrier – it’s human beings vibrating, basically.”

Some vibrate better than others, and Gunn – a graduate of the Met’s Young Artists Program – has sung in Chicago, Philly, London, Paris and elsewhere. But except for a “Cosi fan Tutti” at Mostly Mozart in 1994, where he sang in biker’s leathers and spiked heels, he’s rarely performed in New York.

That’s changed. Hot on the heels of “An American Tragedy,” which plays tonight and runs through Dec. 28, Gunn appears next month in the Met’s “The Magic Flute.”

Back home in Champaign, Ill., some folks still don’t know what he does. A neighbor, after seeing Gunn load up his bags once again, was sympathetic.

“Don’t worry, son,” he said. “You’ll be able to hold down a job soon.”