“I’ve never considered myself anything of a mimic or an imitator,” Natalie Portman said by way of explaining her initial nervousness at the prospect of portraying Jacqueline Bouvier Kennedy, first lady of the 35th president of the United States.

“I’ve never played a character from real life that was so well-known,” Portman said on the phone from New York recently. “I knew that I would have to do such specific work to make people be able to believe that I was her.

“To begin, to just be credible, I had to get to a certain level of the voice and the accent, the movement and the look. It was scary, but it was also a fun challenge – to try something that I didn’t think I could do.”

In “Jackie,” the 35-year-old actress not only gets the voice and the accent, the movement and the look right. She finds something deeper: the psychological and emotional core of a woman, an American icon, in the throes of cataclysmic tragedy.

No standard biopic, director Pablo Larrain’s “Jackie” offers an intensely close-up portrait of the first lady in the days surrounding the assassination of John F. Kennedy in Dallas on Nov. 22, 1963. Mixing historical fact and archival footage (and eerily precise re-enactments) with an almost hallucinatory speculative take on what was going through the White House widow’s head – her grief, her shock, but also the fierce control she maintained over the shaping of her husband’s legacy – the film is bold, breathtaking.

It is also quite literally in your face. The camera frames Portman’s Jackie so she fills the screen – as though by putting the lens right up to her, Jackie’s thoughts and feelings would be revealed.

“Pablo had told me that to achieve the sort of psychological portrait of this woman that he was going for, he really wanted to be very, very close to her,” Portman said. “To really get inside her head. To get as close as possible.”

So, more so than most productions she’s been involved with – even “Black Swan,” the ballet-world psychodrama that won her an Oscar for best actress in 2011 – Portman had to work with the camera in intimate proximity.

“When you’re being filmed that close, the camera is right next to your head, so it’s kind of hard to be oblivious to it,” Portman said. “But that was cool, because the director of photography, Stéphane Fontaine, was also the camera operator, and he was emotionally present. I could communicate with him and have him be like another person in the scenes with me, almost like another actor.”

A key component of the film, returned to again and again like the refrain of a sad song, is Jacqueline Kennedy’s famous guided tour of the White House – taking the TV audience, 56 million viewers – on a room-by-room survey of the nation’s storied edifice and its artwork and furnishings. Portman used the real footage from the first lady’s 1962 guided tour, in the company of CBS newsman Charles Collingwood, as an essential element in her preparation, her coming to terms with the woman she would play.

“I watched and listened to the White House tour obsessively,” she said. “I would listen to it while I was running and while I was cooking and just whenever I could. Because we were really re-creating it with great fidelity, so I was figuring out exactly where she took pauses and where she stumbled over a word. And then just practicing that, those scenes, for the re-creation of the White House tour – that helped me understand the accent and the voice, but also something more about Jackie, who she was, who she was trying to be.”

Portman, who actively campaigned for another former first lady, Hillary Clinton, in the weeks leading up to the Nov. 8 election, says Jacqueline Kennedy changed and challenged the role of the first lady in the eyes of Americans.

“She took it very seriously, and was one of the first ones, after Eleanor Roosevelt, perhaps, to really set an agenda and create a policy as a first lady. She was focused on promoting and celebrating the historical and artistic culture of the United States … I think that she set the precedent for first ladies after her to really have a very clear agenda. She accomplished so much in only two years.

“And I think she was very aware of how she was perceived. When they were on the campaign trail, many in the Kennedy camp thought of her as a liability. You know, they thought that people saw her as a snob. That the typical American housewife couldn’t relate to her, because she had these fancy French clothes and she spoke French and wore her hair in a really wild way.

“And then, of course, when they got in office, all these things that everyone thought were bad suddenly became like trends, and everyone was copying her. Her influence was immense.”

Portman, who is married to Benjamin Millepied, the French choreographer she met while filming “Black Swan,” is expecting her second child. (The couple have a 5-year-old son, Aleph.)

Since shooting “Jackie” last year, the actress has worked with “Ex Machina” director Alex Garland on a new science-fiction project, “Annihilation.” Over the summer, her feature directorial debut, an adaptation of Israeli writer Amos Oz’s “A Tale of Love and Darkness,” was released. (She also starred.)

She plans to direct again. “I’m in the throes of making that happen,” she said.

“Jackie” – with its look back at one of the darkest times in America’s past, and its elegant but shell-shocked fulcrum figure – strikes a nerve.

“That’s one of the things that’s amazing about Pablo’s interpretation of this story is that he allows Jackie to be many different things at different times and take on different roles – like every human does, and particularly every woman, I think … You do have to be many, many things – but not all at the same time, but in different situations with different people, you play these different roles.

“And even that scene where she’s trying on all the different dresses” – a fierce, frenzied moment after the assassination when Jackie finally sheds the blood-and-brain-spattered pink Chanel suit and tries on and discards a series of outfits – “it’s like all these different characters examined at once: Who you are for other people, who other people think you are, who you want them to think you are, who you actually are, who you want to be, who you think you’re supposed to be.

“There’s such a splitting of the self … . And it’s so rare to get to really portray that, for a female, on screen.”