For this role, he was willing to adapt

It was a roll of the dice for director Spike Jonze, casting Chris Cooper, an actor identified mostly with button-down roles, as the skanky South Florida wild man John Laroche in his new film “Adaptation.” As portrayed on-screen, the freewheeling orchid expert is part scientist, part con man -- and sexy, even though he’s missing his front teeth.

“Laroche could have been played as a swaggering cartoon character -- the cat that swallowed the canary,” Jonze said. “But, because he has so much going on inside, Chris brought a deep, broken quality with a lot of humanity. And you trust him, as a person. It’s the Harrison Ford kind of thing.”

The gamble has paid off, given the critical acclaim that followed: year-end awards, Oscar buzz and reviews that are hard to come by. The movie revolves around a self-doubting writer (Nicolas Cage) struggling to transfer “The Orchid Thief,” a bestseller by New Yorker journalist Susan Orlean (Meryl Streep) to the screen.

Laroche poaches a rare “ghost orchid” from a state park in the Everglades in an ill-fated attempt to clone the plant. Reading about his arrest, Orlean tracks him down and, bored with the Manhattan literary life, becomes enamored of his abandon and passion. In the course of researching her story, he becomes her unlikely love interest. (Like all the characters in the film, Laroche is based on a real-life subject but filtered through screenwriter Charlie Kaufman’s active imagination.)

Though the character is the opposite of his own introverted demeanor, Cooper never doubted that he could play Laroche, a type he says he knew from personal experience. Growing up in Kansas City, Mo., he encountered similar folks from the Ozarks. Now living in Massachusetts, Cooper says there are smart, funny lobstermen there who, with the proper education, could have “ruled the world and gone on to become CEOs.”

The initial challenge: convincing Jonze he was right for the part. Watching a “name” actor leaving the audition, he realized the job wasn’t his for the asking.

Because the character was so wide-ranging, Cooper went out on a limb, delivering a variety of interpretations at the 2 1/2-hour tryout -- and the shoot. In the scene where Laroche picked up Orlean in his car, for instance, the actor played it both as “the smartest guy in the world -- you’re lucky to be in my presence” and as a “man intimidated by a New Yorker journalist who probably regards him as a piece of Florida trash.” Not until viewing the final cut two months ago did he know what choices Jonze made. (For that scene, Jonze went with the arrogant approach.)

The Los Angeles Film Critics Assn. and the National Board of Review have given Cooper their best supporting actor awards. Next month, he’ll also be competing for the Hollywood Foreign Press’ Golden Globe and a “Critics’ Choice” award from the Broadcast Film Critics. Whether the actor goes on to win the Big One, or not, his freewheeling, almost raffish interpretation of Laroche has been hailed as a clear-cut departure from his usual screen portrayals.

Since appearing in John Sayles’ “Matewan,” (1987), Cooper has inhabited a series of personas he calls “concealed”: hardened Texas sheriff (“Lone Star”), repressed military man (“American Beauty”), stern father (“October Sky”), and humorless spymaster (“The Bourne Identity”). Next time out, he returns to the “laconic” mode, portraying a down-on-his-luck horse trainer who prefers animals to people in Gary Ross’ “Seabiscuit,” due out from Universal Pictures next summer. His normally sandy hair is cut close and dyed “old man yellow,” for the part.

“I don’t know if I chose those roles or they chose me,” the 51-year-old actor said over dinner at his West Hollywood hotel. “It’s not a source of frustration. I’m thrilled with my body of work. But it’s only the young directors, the first-time directors, the foreign directors who’ve taken a risk, refusing to accept me as just one thing.”

Though Cooper didn’t meet Laroche until the premiere, five hours of videotape provided clues about attitude and body language. To capture the man’s frenetically lean, wiry physique, the actor took off 20 pounds in three weeks, getting down to his high school weight. In some areas, though, Laroche -- atypically reserved on the video -- needed to be punched up, Cooper was convinced: “Playing a mirror image of him would have been a disservice. He was a starting point,” he says.

Known for immersing himself in “homework” and scrawling all over his scripts, Cooper hung out at the Boston Flower Show for several days and visited estates with greenhouses. Repeatedly reading Orlean’s book provided an additional “road map.” That the tooth-deprived, stringy-haired Laroche (a look achieved by “Halloween teeth” inserted over his own and nine hours’ worth of hair extensions) is perceived as a sex symbol is an endless source of amazement.

“It scares me,” maintained Cooper, casually attired in a black sweatshirt and jeans. “If the female public says that, they befuddle me, as they have all my life. I don’t think Orlean would have fallen for Laroche were it not for that fictitious drug she took.”

A serious sort who tends to “berate” himself, Cooper said he learned a lot from Streep. “A couple of weeks into the shoot, things weren’t going well and I was mumbling to myself,” the actor recalls in a soft, measured voice suggesting his Midwestern roots.

“I heard this little voice behind me -- ‘stop whining!’ It was Meryl. Her attitude: ‘You’re lucky to have this part ... enjoy! It’s not reconstructive surgery.’ She’s also forgiving of herself. This doesn’t work? La di da -- try that! I’ve never had as much fun working with an actor.”

Still, Cooper acknowledges, he was overwhelmed by the prospect of the nude scene -- his first. “There was Meryl and there were more than 30 new camera people, most of them women,” he recalls with a grin. “They were called in to make sure the scene was covered well. Trying to make me feel more comfortable, they gave me a little, flesh-colored sock. It was almost more embarrassing to wear it, but out of respect for Meryl, I did.”

Shyness was an ongoing problem for Cooper, the son of a housewife and a doctor-cattleman. While studying at the University of Missouri, he vowed to get “unblocked.” Taking dance classes at nearby Stephens College, he was one of only three men amid a roomful of women. Plieing across the floor everyday, he made a “complete fool” of himself, he says -- helping to overcome his inhibitions. Acting was another means of expression -- “theater, as therapy,” he says. Post-graduation, in 1976, he headed for New York where he studied with Stella Adler and Wynn Handman. To pay the bills, he worked in construction, served as a janitor and, as a chauffeur, drove “well-to-do gentlemen to their cottages in Long Island.”

After 12 years of stage work, including seasons at the Actors Theatre of Louisville and the Seattle Repertory, Cooper landed the lead role of the pacifist union organizer in “Matewan,” directed by Sayles. (The director said he liked the actor’s “haunted” quality, the suggestion of a “past.”) Following his 1991 portrayal of a construction foreman in “City of Hope,” another Sayles film, Cooper played supporting roles in studio fare such as “Guilty by Suspicion” and “This Boys’ Life.” Still, Hollywood didn’t know what to do with him.

Sayles’ “Lone Star” (1996), written with Cooper in mind, was a breakthrough, of sorts, sending a flood of scripts his way. (“A face made for honesty, a body made for sin,” an Entertainment Weekly critic said of his portrayal of a sheriff who suspects his lawman-father had been up to no good.) Three years later, the critically acclaimed coming-of-age drama “October Sky” was supposed to reel in his first wide audience. That scenario was revised, however, when the picture failed to take off.

Cooper is open to leading-man roles, of course. But ensemble work is still a strong draw. In May, he’ll be seen as a university professor in HBO’s “My House in Umbria,” the story of an eclectic group of people thrown together after a terrorist attack. And when it comes to raising his profile, living near Plymouth, Mass., rather than in the film capital of the world certainly hasn’t helped.

“I suspect that a lot of studio executives still think of me as ‘what’s-his-name,’ ” he said. “And when Steven Spielberg came to the ‘Seabiscuit’ set, it was clear he wasn’t aware of my work before ‘American Beauty.’ I didn’t take that as a slight. I don’t go to the studios with producers and directors. I don’t rub elbows with actors. Even Elizabeth Pena, who I made love to in ‘Lone Star,’ didn’t realize I was in ‘American Beauty,’ until she saw the credits.”

Spending time with wife Marianne and 15-year-old Jesse has provided instant perspective. Mentally astute, his son uses a wheelchair because he has cerebral palsy. Jesse’s “the best thing that has happened to us,” the actor says, speaking at length about the family’s victories: a successful battle to get Jesse mainstreamed, a computer that helps him communicate, how well he’s doing in school.

“Like many husbands, I was reluctant to have a child, but Jesse has instilled in us what’s really important,” Cooper said, with the same passion he brings to Laroche. “He seems so normal to us, now. And what a great teacher: His patience is extraordinary and, because he’s so limited, he’s very, very, focused. At the expense of sounding ghoulish, Jesse has fueled the characters I’ve played. He’s filled my emotional life.”

Though the recognition for his work in “Adaptation” is sweet, Cooper says, it’s not the main course. That’s what Oscar contenders usually profess, but he’s believable -- as ever.

“These awards are a midlife adventure,” the actor says. “But it’s always been a good ride. I just want to keep working. No more, no less.”