THE PERFORMANCE

When it came time to cast a small but pivotal role in the movie adaptation of Cormac McCarthy’s bestselling novel “No Country for Old Men” -- a down-home West Texas trailer park housewife who serves as one of the cerebral thriller’s moral compass points -- the Coen brothers did what any self-respecting oddball auteurs of their stature would do. The Oscar-winning writer-directors chose an actress whose native accent is as diametrically opposite the written character’s laconic Texan drawl as just about any in the English-speaking world: Glasgow, Scotland-native Kelly Macdonald.

But initially, the movie’s Texas setting seemed like no country for a young Scot -- even for freethinkers like the Coens.

“They were confused as to why I was sitting in the room with them to play a West Texas girl,” Macdonald, 31, recalled with a giggle. “It’s kind of understandable. I’m not the obvious choice.”

Even though the actress is best known in this country for playing Ewan McGregor’s jailbait girlfriend in the 1996 junkie dramedy “Trainspotting,” Macdonald has had to sublimate her Scottish brogue for other parts. She’s done Welsh (“House!”), Irish (“Intermission”) and even a Midwesterner (for a stage production of “Hurlyburly”) -- although not every acting excursion outside her natural dialect has left her feeling at ease.

“With so many other jobs, I’ve been a bundle of nerves, not happy at all in the voice department,” she said. “I can get to the end of a job and not ever relax. Sometimes it’s harder than others.”

But in “No Country” (which opens in limited release Friday), as the long-suffering wife of a down-on-his-luck Vietnam vet (Josh Brolin) who stumbles on $2 million in drug smuggler cash and goes on the run from a murderer for hire (Javier Bardem), Macdonald sounds as Texan as Lyndon B. Johnson.

“For some reason, the West Texan accent really sat well with me,” Macdonald said. “I felt comfortable from the first reading.”

For the role, she brought a lived-in vitality to her scenes with Brolin that translates into a convincingly intimate on-screen rapport -- one rooted in conflict. Macdonald’s Carla Jean Moss is skeptical of her husband Llewelyn’s decision to take the money and run, yet worried to her core about his survival. She mistakenly undercuts his choices to disastrous effect while still outwardly standing by her man.

Still, to hear Macdonald tell it, landing the part was much more difficult than playing it.

“I want to say that I sweated long and hard, but it was really easy,” she said. “My dialogue coach was on set, but to me, he said, ‘You’re totally fine and don’t need my help.’ He brought along a documentary -- an audiotape of people from West Texas talking. So the hardest part wasn’t so hard. You sit in your hotel room, talking yourself to death.”

Likewise for one of the film’s climactic scenes -- Macdonald’s emotional face-off with Bardem’s character, Anton Chigurh -- in which she tries to reason with him not to put a bullet in her head.

“I had to open the door and Javier’s sitting there in the chair. That was enough,” she said of what got her in the right mind-set. Even though Macdonald’s name has already started cropping up in the best supporting actress category on more than a few Oscar handicapping lists, she’s quick to dispel the idea that the part required much effort.

“Cormac McCarthy’s dialogue is very obvious -- you can hear it in your head,” Macdonald said. “The script’s so good, it would be hard to go wrong. It was one of the easiest jobs ever.”

chris.lee@latimes.com

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Where you’ve seen her

Kelly Macdonald has appeared in numerous British indie movies, including 1996’s “Trainspotting,” but she’s hardly a household name in the U.S. The talented Scottish actress is primarily known for character turns in mainstream fare such as “Finding Neverland” (as Peter Pan), “Nanny McPhee” and “Gosford Park,” as well as the title role in the 2005 HBO romantic drama “The Girl in the Cafe.”