As a power couple, the Roosevelts make the Clintons look like underachievers. Franklin Delano Roosevelt was the most powerful president of the 20th century, and his wife, Eleanor, wielded her own power behind the scenes, a feminist who championed women and the disenfranchised.

So how does one play these icons? With humility and, for Bill Murray as FDR, with liver spots on his forehead, a jutting chin, a period haircut and a long cigarette holder. Turning Olivia Williams into Eleanor required a prominent set of buck teeth, a fat suit and an undergarment that makes it look as if she could tuck her breasts into her waistband.

Murray and Williams play the first couple in “Hyde Park on Hudson,” a film that is the opposite of a biopic — a micro-pic. It homes in on a single weekend in June 1939, when the president hosted the king and queen of England at his family's country estate in upstate New York. Also on hand are his mother (Elizabeth Wilson), his wife, and a distant cousin and neighbor, Daisy Stuckley (Laura Linney), with whom Roosevelt, an unrepentant womanizer, is having an affair. (Historians are less certain than the movie, written by Richard Nelson based on Daisy's diary, that the affair happened.)

In rehearsals, Murray and Williams came to the same conclusion about how to portray the Roosevelts, who by 1939 were no longer intimate (she couldn't abide his infidelity) but remained close.

“It was very much the idea that they were friends, and they would hold hands and that they had this 30-year marriage behind them,” Williams said.

Contributing to their portrayal “is the fact that I had worked with Bill before and I have known him for 14 or 15 years,” she said, referring to the 1998 “Rushmore,” in which she was cast as a teacher at a quirky private school and he as a benefactor who is attracted to her.

“Bill and I stayed friends. We stayed in touch. Even though I hadn't seen him for a long time when we started rehearsals, we fell back together and went and saw some theater in New York and again it was that familiarity we have with each other. When you have worked together, you are like old battle comrades.”

Williams called her co-star “one of the most serious and conscientious actors I know. He worked very hard on FDR, on every aspect of him. He is not the stand-up guy from 'Saturday Night Live.'”

Murray won't own up to any huge preparation.

“I hate to give away my secrets. I do almost nothing. But I did a lot of reading. I studied the accent of the area and worked with a fellow who was a specialist,” he said at a news conference during the Toronto International Film Festival.

He did reveal that he looked to his sister, who was stricken with polio as a child, for an example of how to buck up when struck by misfortune. She wore excruciating leg braces like FDR's, yet “she didn't complain about anything,” Murray told the Chicago Tribune.

Roger Michell, the award-winning director of “Notting Hill” and “Persuasion,” said Murray always seemed an obvious choice for Roosevelt even when “everyone was telling me he wasn't. I mean, he shares his physicality with the president and, more important, the film was never intended to be a kind of Madame Tussauds' version of history.”

“He has this superabundance of easy charm that Roosevelt had. He has the same massive, scruffy charisma — the charisma of a man in a rumpled linen suit.”

Roosevelt is “someone who, for all his frailties — and indeed the film suggests appetites and frailties — is forgivable because of his sweet nature. Roosevelt did an incredible job to keep so many people around him so happy. It feels like he operated a kind of harem.”

Michell found himself surprised by “the level of FDR's playing around, although why one is surprised, given the conduct of another American president, I don't know.”

Williams has thought about what Eleanor's reaction might have been to Daisy, whether her husband was having sex with her or just flirting.

“I literally played it that she just functioned on a different plane. It's like when you let a house become messy and you just don't see the mess anymore,” she said. “She just didn't look. I think she cried about him quite a bit, but she felt her pain in private, and in front of other people she used her position as his wife.”

She and her husband were a formidable team with the ability to make anyone feel comfortable — even British royalty. Murray has talked about the importance of showing FDR with a twinkle in his eye. It was his secret weapon. He was a master at making people believe in him and accede to his wishes. On the weekend depicted in the movie, King George VI's task was to persuade the president to support England in its impending war with Germany.

Roosevelt instinctively knew what to do.

“He treated him like the father the king had never had,” said Michell, who delved into writings from the time to determine how to play this scene.

This is the same king, nicknamed Bertie, who appears in “The King's Speech.” If audiences don't know this, “they might think all British monarchy stutter,” said Williams, who is British — a fact that didn't stop her from pursuing the role of Eleanor.

She recalls that Michell was skeptical at first.

“He said, 'You are British,' and I said, 'Don't be stupid. I am one-eighth American and Eleanor was educated in England. And secondly, my husband is American, so I am half American.'

“Then he tried to flatter me out of it by saying I was too beautiful. I said, 'Bollocks. That is only because she was dowdy looking and didn't care. When I don't care, I look very much like her.'”

The first lady's lack of concern about her appearance seemed to put other women at ease.

“If someone arrived looking beautiful, then she felt, job done. She had made the person feel good,” Williams said.

Ruthe Stein is the San Francisco Chronicle's film correspondent.