"Doubt" is, obviously, not a movie about clearcut answers.

It's set in 1964, in a Bronx parochial school, and Father Flynn -- fond of secular music, and of keeping his fingernails effeminately long -- is hardly a favorite of the ramrod-straight Sister Aloysius. So when the priest's relationship with a troubled young boy seems, vaguely, "inappropriate," the good sister is quick to think the worst.

But what does the actor who plays Flynn think?

"I kind of don't understand the question," Philip Seymour Hoffman says, a little testily, over the phone -- after, perhaps, a too-long morning of interviews. "Every character I play, they've lived a life. I have to make decisions about them ... I don't know. No other part that I've played have people asked me that question."

Well, I tentatively suggest, the difference is that in the actor's other recent films -- "Before the Devil Knows You're Dead," "The Savages," "Capote" -- the characters were fully revealed on screen. Here a central fact is withheld: Is Flynn a pederast, or merely persecuted? The audience is encouraged to wonder, but did the actor have that luxury?

"The question doesn't make any sense," he says.

Stubbornly, I try once more. I tell Hoffman that I assume he had to arrive at his own solution to the mystery before he could begin to play the character. I'm just curious if he spoke to playwright (and director) John Patrick Shanley about it first, or deliberately chose not to. I don't necessarily want to know what Hoffman decided, but ...

"Well, if you're not interested in knowing the answer, why even ask the question," he asks.

At which point I drop the topic entirely. Hoffman, who had an Irish Catholic mother and a German Protestant father, may not have had his own parochial education ("I went to Sunday school, but I didn't do the whole altar-boy thing.") But I did, and I can recognize when I'm stuck in a can't-win debate. The Christian Brothers were experts at it.

Besides, we only have half an hour. And there are many more things to talk about than whether Hoffman thinks his character in "Doubt," opening Friday in New York, is a villain or a victim. There's the road that led him to acting. His approach to the profession. And an astonishing array of performances, from Eugene O'Neill on Broadway to "Mission: Impossible III" on the big screen.

Hoffman, 41, grew up in Fairport, N.Y., the son of a businessman and a family-court judge, and "just fell in love with the theater" at 12 or 13. "I didn't even want to be an actor then," he says. "I was just a big theater fan, just really enjoyed a good play. But then in high school, I started auditioning and I loved the camaraderie of it, the people, and that's when I decided it was what I wanted to do."

He ended up in drama school at NYU, where the expenses -- $21,000 a year then (it's more than twice that today) -- were absolutely daunting, even to an upper-middle-class kid.

"My parents were very supportive, but they didn't quite have the finances to take care of college, so I had to help myself in that arena," he says. "But I loved being at NYU. What's great about it, if I can promote it a little bit, is that you're really part of the city. The theater is all around you, and if you want to rub your shoulders against it, you can, and if you want to try for usher jobs, or internships at working theaters, you can. And I did all that."

Hoffman had his own experimental acting company -- the Bullstoi Ensemble -- while still on campus, and after graduation went out for all the usual "off-off-Broadway stuff." But the stocky, strawberry blond was nobody's idea of a leading man, and it took a while to find a place in the commercial mainstream.

"Like everybody else, I did an episode of 'Law & Order,'" he says. "I went out to LA for awhile, and tried to get into films. But it wasn't until 'Scent of a Woman' that I started working regularly. There are many different things that keep propelling you forward, but that was a major part of the beginning. I really felt like I'd won the lottery."

It was a lottery that paid off for audiences, too as very quickly, Hoffman began exploring a vast country of characters -- lonely misfits and uncomfortable oddballs -- that many other actors wouldn't (or couldn't) play.

The needy gay filmmaker in "Boogie Nights," the wretched rich boy of "The Talented Mr. Ripley," the gas-huffing widower of "Love, Liza," the miserable onanist in "Happiness," the mincing genius of "Capote," the obsessed director of "Synecdoche, New York" -- what could be, in other hands, a gallery of grotesques became, with Hoffman's artistry, a series of richly human, nakedly honest portraits.

Portraits that, once he hangs on the wall, he says he's able to forget.

"I remember in acting class, a teacher once telling a student, 'You do know you're not really that person, don't you.'" Hoffman says with a laugh. "Which is funny, it's so obvious -- this is not you, this is not your life -- but for some actors, the characters they play stick with them. But for me, the minute I've wrapped it's like, 'Goodbye, I don't want to feel you anymore.' They just go away, immediately."

Which is, probably, an important way Hoffman has of staying sane, and in a decade-long relationship with his girlfriend and their three children -- you wouldn't want to bring the guys from "Before the Devil Knows You're Dead" or "Red Dragon" or "Punch-Drunk Love" home with you at night.

Still, the work lingers.

"What I do find is that the ideas stick with me," he says. "Like with this film, the whole theme of the new and the old battling, and change happening -- if the ideas are interesting ideas, the way they were in "Synecdoche," they linger. Or, occasionally, if they're pertinent to what you're going through yourself -- that stays with you. But the rest of it just goes."

What also stays with him are the people he's worked with -- directors like David Mamet, Sidney Lumet and the Coen brothers, co-stars like Robert De Niro, Al Pacino and Ralph Fiennes.

"You learn things from everybody," he says. "You're always learning. Acting isn't like riding a bike -- every time you start, you're starting from scratch. It's more like playing golf, where you know you know how to swing the club, but then you tee off and you hook it and you have to kind of stand there and think, Am I holding it right? What am I doing wrong this time? There are all these little subtle things that affect the big picture, and every time you're working you really have to go back to being a beginner, and go through everything again to get it right."

If acting is like golf, though, Hoffman's last two films have been a little bit like LPGA events. On "Synecdoche," he worked with an honor-roll of femme indie icons including Emily Watson, Hope Davis, Catherine Keener, Diane Wiest and Samantha Morton; on "Doubt" he shares powerful one-on-one scenes with Amy Adams and Meryl Streep.

"It's been pretty cool," he happily admits. "I've been able to work with some really great women -- smart, vibrant, imaginative women. We did Q and As after some 'Synecdoche' screenings and I was literally the only guy up there, surrounded by all these wonderful women. And I was oddly at ease with that."

Perhaps it's because he's oddly at ease with himself.

He hasn't always been. He had more than the usual student-share of substance issues when he was at college; he can still, obviously, turn cranky or cold in an interview. And he seems congenitally incapable of turning down a good part -- working so obsessively that, come awards season, he's often competing with himself (last winter alone he had "The Savages," "Charlie Wilson's War," and "Before the Devil Knows You're Dead.")

"I know, it's too much, isn't it?" he says, apologetically. "I've really got to find some down time."

It's not easy (Hoffman's also the co-artistic director of New York's LAByrinth Theater Company). When he does take time off, though, he spends it with costume designer Mimi O'Donnell and their three children -- all under the age of 6 -- getting the kids breakfast, taking them to the park, walking around the city. And trying to explain what it is that he does, and why strangers will sometimes run up in the street just to shake his hand.

"My 5-year-old, he'll come with me to the theater, so he understands that part of it," Hoffman says. "'We'll dress up, and you be this character and I'll be this one' -- that makes absolute sense to kids. But movies are difficult. 'Why are we in this warehouse? Why aren't there seats? Isn't this supposed to be a show?' I've taken them and they watch for a bit and it's like, 'Yeah, great Daddy, that was neat. Now -- can we please go home?'"

Stephen Whitty may be reached at swhitty@starledger.com or (212) 790-4435.