NEW YORK — “Has the play started yet?” a waitress asks a bundled-up Kevin Bacon as he takes a seat in a bustling Upper West Side breakfast cafe, where he and his wife, Kyra Sedgwick, are regulars.

“Feb. 7,” replies Bacon, who promptly strips down to a ratty T-shirt and orders up an eggs-and-toast combo with — what else? — a side of bacon. “I saved room,” he says with a rare grin as he places his cell phone and Ray Bans on the table. (It rings twice during the interview but Bacon politely ignores it.)

Judging from the chunk Bacon has just bitten off in his professional life, he will need every ounce of energy he can get. He is starring in the one-man show, “An Almost Holy Picture,” a Roundabout Theatre Company production, that is currently in previews. Of course, it is ironic that Bacon — the actor forever famous for his six degrees of separation from every other Hollywood actor — takes the role that will connect him to no one. But for Bacon, who got his start in the late Seventies at New York’s Circle in the Square Theatre and made his Broadway debut opposite Sean Penn in “The Slab Boys” in 1983, it’s a return to his roots.

“It was a good show last night. It felt good,” says Bacon, who completed the play’s fourth run in front of an audience just 12 hours earlier. At 43, his boyish appearance is still intact: the spiky hair, jutting cheekbones and super lean physique. Only his eyes, edged with the faintest of wrinkles, betray him. His deep voice is scratchy, showing signs of the previous night’s wear. “A lot of what the previews have been, as far as I’m concerned, is me discovering my relationship to the other cast members — which is you. I felt like I really took a step toward understanding what the connection to the audience could be.”

In the play, written by Heather McDonald, Bacon plays Samuel Gentle, a soul-searching ex-priest and church groundskeeper, whose beloved daughter is born with congenital hypertrichosis lanuginosa (lanugo), a rare genetic condition that covers her entire body “in a white-gold swirl of hair.” The disease is passed on from father to daughter or mother to son, which leaves Samuel grappling with guilt and questioning the existence of God in the face of her disability — and what he deems his failure.

The dramatic role Bacon tackles is a departure from many of the lighthearted roles he’s best known for in his 40-plus films, which include “Footloose,” “Flatliners,” “A Few Good Men” and “Apollo 13.” But according to Bacon, the play struck a note.

“The fatherhood connection for me was very strong,” says Bacon. He and Sedgwick have a 12-year-old son, Travis, and a 9-year-old daughter, Sosie. “I really connect to the fact that this guy is doing his absolute best and trying to do the best job he possibly can as a father — as most of us try. Yet he always manages to f— up along the way, which is what most of us do I think, to a certain extent.”

The character’s spiritual journey is a key element to the play, but one that didn’t initially resonate with Bacon. “I don’t have a very active spiritual life,” he shrugs as he douses his plate with Tabasco. “I don’t go to church. I never have. I don’t really consider myself a part of any religion and yet when you’ve experienced birth, death, tragedy — you know sometimes you start to think about finding some kind of spiritual center for yourself, whatever that may be.”

Interestingly, Sept. 11 played a part in bringing “An Almost Holy Picture” to light. Both Bacon and Michael Mayer, the resident director of the Roundabout Theatre who had directed the play in La Jolla, Calif., were attached to the project but hadn’t found the right Manhattan venue. After the terrorist attacks, Sondheim’s musical, “Assassins,” which was scheduled to open at Roundabout’s American Airlines Theatre in February, no longer seemed appropriate. The slot opened up and Bacon headed to the theater, where he did a reading of the play.

“I felt more rooted to the city than ever,” says Bacon. “And this was an opportunity to work at home. I felt very, very affected by the tragedy and the play talks about that and deals with that. Man questioning God and the existence of God in the face of tragedy — that’s really what it’s all about.”

For an actor who — let’s face it — hasn’t always enjoyed the glow of critical success, wasn’t Bacon concerned with going solo?

“I like challenges,” he offers. But 100 minutes of dialogue without relief from a single character sounds like self-torture. “Learning the lines is without a doubt the easiest part of being an actor,” he scoffs. “If it was just about learning the lines, any asshole could do it. It’s about feelings, it’s about becoming other people.”

Bacon does have something to prove. After all, the parlor game, the “Six Degrees of Kevin Bacon,” all but solidified his legacy as the ultimate B actor.

“I never thought it would last this long, honestly,” says Bacon, who admits that early on, the game plagued him with self-doubt. “I kind of felt like it was a joke at my expense. This is the way an actor’s head works — you think, ‘Can you believe this loser can be connected to everybody in the acting world?”‘

But now, as time has gone on, Bacon says that he finds the concept amusing.

Self-doubt has overshadowed Bacon in another arena. He has logged hundreds of hours of live performances with his band, the Bacon Brothers. Last summer, he and brother, Michael, played more than 50 dates while touring the country to promote their third CD, “Can’t Complain.” In May, the duo plan to record a live disc that is a compilation of their work.

“Standing in front of people with a guitar and singing songs that you wrote about things that personally matter to you is probably the most naked you can feel as a performer, in my experience,” says Bacon. “Doing a play and playing in a band are fairly closely related. You have this evening with this group of people that is special and magical and will never be exactly the same again. And when the lights go down, you take a deep breath and walk out there.” He pauses. “Anything could happen.”