BEVERLY HILLS, Calif. — Colin Firth was nominated for an Oscar for best actor this year for “A Single Man.” As we know, Hollywood insider Jeff Bridges took home the Oscar, but Firth was “genuinely thrilled at the nomination and genuinely relieved when it was over. The stress is something else. So are the questions posed after you’re nominated.”

The movie, of course, is the long- delayed screen version of Christopher Isherwood’s acclaimed 1960s novel (dedicated to fellow gay author Gore Vidal). And it marks the directorial debut of openly gay American fashion designer Tom Ford, who also adapted the book and coproduced the film.

In the movie, Firth, a native of England who is himself heterosexual, played a grieving professor living in ’60s Los Angeles. He notes: “I got to play British. Had I played American, well, I can do it, but . . . One question I got a lot at nomination time was, ‘How difficult was it to play a gay character?’ They still ask that. A lot. I would reply with something like, ‘That’s a very Hollywood question,’ and most of them didn’t know what I meant.”

Firth wasn’t the only one taking on an accent across the pond from his own. “In our film, the leading lady was Julianne Moore, who’s American. She played a London character, too. And we had two Brits playing American young male characters. So I was the only one sounding like myself.”

The movie covers a day of intense torment in the life of a man whose younger male life partner had been killed in a car accident. The picture is relatively faithful to the novel but adds one dramatic twist, to maintain suspense. Ford had said Firth was the only actor he had in mind for lead character George, and the two have much in common: Both Firth and George seem reticent and serious — at times studious. Neither seems very spontaneous or trusting — there’s always a reserve. Is that a British trait, or simply part of Firth’s character?

“I don’t know that I’m reserved, by my standards,” he says. “By Hollywood standards, perhaps. But I found George a very easy character to identify with. He is of course grief-stricken, but for the most part he doesn’t show it. It’s the times — we’re talking about the 1960s, when things were different for heterosexual people and more so for homosexual people — and he is a college instructor and aware of it.”

Did the Hollywood contingent ask many questions about the “risk” of playing gay or how he went about it?

Firth laughs. “The ‘how’ is another one of those questions. How does one play a heterosexual? It depends on the individual character. As for risk, very often, at least in Hollywood film, when an actor who is not gay plays a gay character, he winds up nominated for awards. If he is gay playing gay, if he is gay playing not gay, then that actor is not usually nominated. That was brought to my attention during filming.”

Indeed, Firth told reporters at the movie’s U.K. premiere in February that he believes the Hollywood system keeps gay actors in the closet, because they face discrimination within the industry. “There are not a lot of openly gay leading men,” he was quoted as saying.

Firth has played homosexual roles before. In one of his early films, 1988’s cult favorite “Apartment Zero,” Firth played a gay Brit with a crush on a brash, handsome American who is revealed to be a rightwing terrorist. And his character in 2008’s smash-hit musical “Mamma Mia!” was also gay. Firth says he is unsure why he gets picked for such roles but suggests there may be “a shy quality some people seem to attribute to me.”

“Perhaps being British — to Hollywood, that’s close enough,” he chuckles. “But a good role is a good role. Or perhaps because I do it well. I do it naturally, which is to say I don’t make an effort to ‘be’ gay, because that isn’t reality. Unless, well, you’re Boy George and therefore feeding off the stereotype.”

Firth, who turned 50 on Sept. 10, married producer/director Livia Giuggioli in 1997, and the couple have two children. Prior to that, he had a son with actress Meg Tilly, with whom he costarred in “Valmont” (1989), the other film version of the 18th-century novel “Dangerous Liaisons,” which did less well at the box office than the one with Glenn Close, Michelle Pfeiffer and John Malkovich. On his private life, he doesn’t speak, because “private means private. My work means opening myself up in character but not necessarily about my real self.”

The actor does have a sense of humor, though, and admits he has rarely thought of himself as sexy, which used to be a requirement for a leading man, at least of the Hollywood variety. Yet he played the romantic — some would say sexy — role of Mr. Darcy in “Pride and Prejudice” (1995). When offered the role, Firth told his brother Jonathan, who riposted, “But isn’t he supposed to be sexy?” (Firth also has a sister, Katie Firth, who is a vocal coach.)

Firth played a different Mr. Darcy in “Bridget Jones’s Diary” (2001) and its sequel. He credits the films with making him a more successful actor than he had expected to become — in short, a leading man.

As a child, Firth bowed as Jack Frost in an English “panto,” and much later was discovered playing “Hamlet” at a drama school he attended for two years. His first professional role was in the play “Another Country” in London’s West End; when a film version was made, he costarred in it (but in another role).

His costar was openly gay actor Rupert Everett. The two men have a rivalry going, whose cause Firth won’t reveal. He also has a semirivalry, that he jokingly laughs off, with Hugh Grant. “No,” he corrects, “Hugh is all right, in his way. Hugh is feuding with Robert Downey Jr., or so I’m told. I don’t have time for feuds.”

Firth is a secure actor who plays what the character requires, rather than trying to seem heroic or be likable all the time. For instance, in “Then She Found Me,” his character, opposite Helen Hunt (who also directed), is often unappealing.

“Helen wrote the character in, you see,” says Firth. “She adapted a novel, adding my character. As the writer-director, she chose for him to be moody, flawed, at times almost vile. I accepted to play him, and I played him as written and as directed.”

Despite his talents, Firth has not worked a huge amount in Hollywood, nor has he ever lived there. “I go where the work takes me, but I am based in England of course, with my family,” he says. “In point of fact, I have lived in the States. For one year. Quite a while ago.” At about age 12.

He’s also lived, as a child, in Nigeria. “One of the great perks of being an actor is travel. Travel to places you’ve wanted to visit and to places you never thought you would visit. For that matter, playing characters you wouldn’t have dreamed of playing — I played (17-century painter Johannes) Vermeer (in “Girl With a Pearl Earring,” 2003). To me, that was having your cake, eating it, and having the frosting on the cake.”

More and more actors are turning their hand to directing — from Clint Eastwood to Ben Stiller — and this is a potential route that Firth does not dismiss entirely.

“It’s not out of the question, and perhaps it is possible when I have more time away from family ties and duties. Directing is beyond full-time. It’s every waking minute of the day, and it’s also before filming and after filming. And I must say, Tom (Ford) should have been up for an award himself (for ‘A Single Man’). Wasn’t he brilliant? The look of the film, the style, the innovations — did you notice the ‘flushes’ he used?” says Firth, referring to an intensification of color while a character is feeling a strong emotion.

“If I had won (an Oscar) — the big, big ‘if’ — I would have thanked and acknowledged Tom first and last. It’s a film to be very proud of, and I think, like the book, it will stand the test of time. I’m certain that in a few decades, when all my films are added up — and the chaff (separated) from the wheat, all that sort of thing — ‘A Single Man’ will be at or right near the very top of that rather long list.”

Is there anything Firth would not do on screen, any risk he wouldn’t take? He laughs. “I might not do full-frontal (nudity) now. I wouldn’t do a musical where I had to carry the burden of musicalizing. When we did ‘Mamma Mia,’ the men in the group became very nervous. Scared, even. And once again, Meryl Streep put us all to shame. Did you see her? Hear her?”

In fact, Colin has a pleasant singing voice (which can’t be said of costar Pierce Brosnan).

“Basically, as you move on in time through quantities of films and roles,” he concludes, “you want something different. Something different so long as you can be good at it — or at least not flop at it. . . . And if you’re working with wonderful people like Tom and Julianne on top of it, you do better than you thought you could; and, well, what more could you want, or should you want?”

“A Single Man” opens Oct. 2.