Anyone approaching “Jackie” looking for a blithely buoyant Jackie Kennedy might be taken aback by Natalie Portman’s performance: Radiating a brittle ferocity and percolating with bitterness, Portman’s character is an uncanny mix of good breeding and furious anger.

“It’s totally understandable,” said the Academy Award-winning actress, whose performance in the film (which opens Friday, Dec. 2) is already generating Oscar buzz. “She was set up to feel she had the brightest future ahead of her and it was all cut down in such a violent, dramatic fashion.”

The role — which focuses on the period immediately after the JFK assassination — was “a great challenge,” said Portman, an opportunity to flesh out an enigmatic character who was “well-known, but in a two-dimensional way.”

Jacqueline Bouvier Kennedy had become first lady of the United States at 31; she would be the world’s most famous widow at 34. “She had the most desirable, most powerful husband in the world, she had adorable children. She was beloved,” said Portman. “And all of a sudden everything was taken away, and in a completely terrifying way.”

“Jackie” was directed by the celebrated Chilean filmmaker Pablo Larrain (“No,” “The Club”) and written by Noah Oppenheim, whose script was chosen best screenplay at the Venice Film Festival this September. Oppenheim, who has worked as a producer for “Today” and “Hardball With Chris Matthews” (and adapted the sci-fi adventures “Allegiant” and “The Maze Runner”), wrote “Jackie” six years ago, on spec.

“I figured the best writing comes from a place of passion,” he said. “She’s someone I’ve been reading about my whole life, and this period is one I’ve been studying for a good chunk of my adult life. I felt I knew a lot about it and had a particular point of view about her, so my best-case scenario was that at least it would be good — if not necessarily have obvious mass appeal.”

advertisement | advertise on newsday

Jackie Kennedy, of course, has obvious mass appeal — her celebrity straddles generations. But “Jackie” is a cerebral, philosophic and spiritual examination of a historical figure perhaps best known for her sense of style.

“It’s not a traditional, glossy, cradle-to-grave biopic,” Oppenheim conceded. “We had a particular point of view of the subject matter and Pablo said, too, that any kind of film that tries to lay claim to a single truth about a person as complicated as Jackie Kennedy is making a mistake. She was really complicated and we wanted to capture her in all her complexity.”

The assassination and the period surrounding it have been “mined creatively” countless times, Oppenheim said. “So you’ve got to be really careful, if you’re treading back into it, about having something unique to say.” Oppenheim wanted to say something about the unknown Jackie: “She’s been portrayed on TV and in films many times and been written about ad nauseam, but it’s most often been in terms of her being a style icon, the relationships to her husband and their complicated marriage. I never thought she’d gotten her proper due for being a political and marketing and public-relations genius and the role she played in crafting the mythology of her husband’s presidency.”

“Jackie” co-stars Peter Sarsgaard as Bobby Kennedy and Billy Crudup as the journalist whose interview with Jackie enables her to begin molding her late husband’s presidency in terms of a lost Camelot. (He’s not called Theodore White, but that’s who inspired Crudup’s character.) Greta Gerwig plays Nancy Tuckerman, the White House social secretary; Beth Grant and John Carroll Lynch are Lady Bird and Lyndon Johnson. Naturally, there are a lot of accents and inflections being tossed around (Boston, Texas . . .) but none as curious, or as much of a signature, as Jackie’s odd way with words.

“It’s really its own thing,” Portman said, when asked to define it. “It’s a New York, Long Island accent, a mid-Atlantic accent. It’s ‘Grey Gardens,’ ” she said, referring to the 1975 documentary about Jackie’s cousins, the Bouviers of East Hampton, who spoke in a similar way. To get a hold on it, said the actress, a graduate of Syosset High School, she availed herself of the famous White House tour conducted by Jackie for the TV networks in 1962; the eight-plus hours of taped conversations with Arthur Schlesinger Jr. that were released only in 2011; and interviews done during John Kennedy’s re-election campaign for the Senate in 1958, which Portman said she found very helpful. “She was very poised but not quite as polished as she would be, and you see her figuring out how to control herself throughout the campaign.”

Control is a key part of the Portman performance; Oppenheim said Jackie Kennedy was “completely panicked” about how she would support herself and where she and the children would live after the assassination; that a woman as prominent as Jackie would have issues of financial independence puts a feminist slant on “Jackie.”

“I don’t think she defined herself as a feminist, especially at that point,” Portman said. “She was famously married to well-known men and known for the men in her life — Bouvier, who was her father, then Kennedy, then Onassis. But at the end she was her own woman. She defines herself as her husband’s wife in the film, but she couldn’t help but be her own woman. She ultimately was the author of her own story.”