Puffing on a chain of Marlboro Lights, Paul Bettany sits near Brooklyn's Prospect Park, somewhat weary from having just flown in from Paris the night before. It was the latest stop on a month-long parade of publicity he's been marching for ''Master and Commander: The Far Side of the World.'' ''Forgive me for looking like this,'' he tells the makeup artist dusting at the bags under his eyes. ''This is somebody who hasn't slept and has talked about himself too much.'' His wife (and Oscar-winning ''Beautiful Mind'' costar), Jennifer Connelly, has accompanied him to this photo shoot. She's carrying their 4-month-old son, Stellan, who snoozes in a Sex Pistols onesie, and whenever the photographer stops to change film, Bettany dashes over to them, pleased to get a hit of real life after weeks of just talking about it.
Bettany, 32, has been sailing a wave of critical praise for his performance as ''Master'''s forward-thinking naturalist Dr. Stephen Maturin, who counters the bravado of Russell Crowe's Capt. Jack Aubrey with his own logic and wariness. But with this acclaim come more interviews, and though Bettany is gregarious and witty, there's something about the demand for personal info that is at odds with the anonymous pleasure he gets from his roles. ''In acting, you have a buffer,'' he says. ''It may well be you, exactly you, on camera, but nobody can actually go, 'That's him!' They can say, 'I bet it is,' but they don't know for certain.''
Bettany was raised in Harlesden, an area he calls ''the slum'' of northwest London, and dropped out of school at 16 to become a busker, singing and playing guitar on the streets. In a year, he grew bored crooning the Beatles' ''Money (That's What I Want)'' for shillings, and enrolled in London's Drama Centre. Part of the reason he shelved any musical aspirations, he says, was that he didn't want the public hearing his personal lyrics.
Well-received performances in the London theater and Brit cinema led to his brutal turn in ''Gangster No. 1,'' his immodest jaunt as an oft-bare-assed Chaucer in ''A Knight's Tale,'' and his first pairing with Russell Crowe, as John Nash's imaginary friend in ''A Beautiful Mind.'' (He also recently wrapped the romantic comedy ''Wimbledon'' with Kirsten Dunst, and he'll soon be seen in Lars von Trier's ''Dogville.'') Though ''Mind'' earned him the most acclaim, it nearly kept him out of ''Master,'' since director Peter Weir was concerned that reteaming him with Crowe might be distracting. ''I thought it would be like borrowing their friendship [from 'Mind'],'' says Weir, who auditioned other actors for the part but came back to Bettany. ''I thought, I would spend a couple of years with this guy sailing around the world.''
But the reunion helped the film, says Bettany, since the actors strove not to duplicate their last interplay. ''In the rush to get your characters on screen,'' he says, ''you can forget that the relationship between the two is a sort of third character. We gave that more thought than we would have had it been our first time together.''