'I really did think it was going to be seven weeks, in and out," says

Frank Langella

, recalling his decision, in early 2006, to star as

Richard M. Nixon

in

Peter Morgan's

play,

Frost/Nixon.

Set for a short run at the Donmar Warehouse Theatre in London, the play - about the series of interviews conducted by talk show host

David Frost

in 1977 with the only U.S. president ever to resign from office - won hugely favorable reviews.

Suddenly, the New Jersey-born Langella, and

Michael Sheen

, who played Frost, found themselves moving to a bigger house in London's West End. In April 2007, the intense tete-a-tete drama opened on Broadway, where Langella went on to nab the Tony Award for best leading actor in a play.

And then

Ron Howard

climbed aboard and decided to make a movie out of it. Langella and Sheen reprise their roles, joined by

Kevin Bacon

,

Rebecca Hall

,

Oliver Platt

and

Sam Rockwell

. The film opens Friday at the Ritz East and the Showcase at the Ritz Center/NJ.

"It's taken actually a little over 21/2 years of my life," says Langella, on the phone from New York the other day.

"So you never know. It's another good lesson in choosing something because you really want to do it, versus because you think it might have commercial potential. . . . Very often you choose projects that you think are going to do great things, and they fizzle and die."

Langella, 70, now finds himself among the contenders for a best-actor Oscar nomination for his performance as the 38th president, forced to step down in the wake of the Watergate scandals.

"He is an epic tragic figure," says the actor, who remembers watching the president make his historic announcement on TV, in August 1974.

"I was sitting on the floor of a little house I was renting in Williamstown, Massachusetts," he remembers. "I was doing a play at the Williamstown Theatre Company, and rehearsal was canceled, or put back for a few hours, so we could all go to my house and watch the resignation speech."

For playwright Morgan, Langella was the only man for the job of portraying the tarnished former commander-in-chief.

"We agreed that he had to be an American, not a Brit, and they came back with half a dozen names, and the director and I immediately felt that Frank should go to the top of the list," recalls Morgan, in a separate interview. "Frank has the physical stature, because Nixon was a tall man, but more than that Frank has this extraordinary stage experience. He is, quite simply, a master. . . .

"And we were thrilled that he said yes. But don't forget, he only agreed to come and do the seven-week run. No one, none of us, could have predicted any of this!"

Morgan, 45, has made something of a specialty of investigating the private lives of public figures. He wrote

The Queen

, for which

Helen Mirren

nabbed an Oscar (with Sheen portraying Prime Minister

Tony Blair

). Morgan adapted

The Other Boleyn Girl

, about

Henry the VIII's

palace love life, and scripted

The Last King of Scotland

, about Ugandan dictator

Idi Amin

. (That one, too, won an Academy Award for its lead,

Forest Whitaker

.)

"It's almost this little genre of its own that's popped up, and I'm not quite sure what to make of it," Morgan says. "Presumably, there's something there about that sort of weird trade-off between a very public figure and their private humanity. The relationship between the personal and the office. For example, the queen is the queen, but she is also

Elizabeth Windsor

, and she's trapped somewhere in between. . . . There's a constriction, a sense of imprisonment.

"And it's the same with the president, as I imagine

Barack Obama

is about to find out. . . . To some degree you are dehumanized, because from the moment you take office you are known as 'Mr. President' and you're known as Mr. President for the rest of your life.

"And yet you are still very much a person."

And it was Nixon the person - his human failings - that led to his downfall, says Morgan.

"If he weren't a paranoid, pessimistic human being, he wouldn't have done what he did in 1972. Because he was never going to lose that election, he was always going to beat

McGovern

; all the polls suggest that. . . .

"He was the architect of his own demise, and yet simultaneously he was a man who was clinging to power at all costs, and that seemed like a really interesting place to go, as a writer."

And if you were to throw that tragically flawed man into a room with a supercilious chat-show host - the "part-entertainer/part-political interviewer" Frost - it seemed that there was potential for something, well, Shakespearean in scope.

"Our humanity will always humiliate us," Morgan notes. "Our needs and desires are so weak, we are so fragile, and just in that sense alone, how easy is it to be human and also achieve greatness when there is so much in our humanity that conspires against greatness?"

Short subjects.

Kristen Stewart

, better known right now as Bella Swan, heroine of that itsy-bitsy teen vampire pic

Twilight

, has signed on to play rocker

Joan Jett

in

The Runaways

, a 1970s period piece about Jett's influential all-girl L.A. band. Stewart will start work on that immediately following

New Moon

, the first

Twilight

sequel, set to begin production early in the new year. (She's going to have to buff up.) . . .

Steven Soderbergh

is segueing from

Che

, the director's epic two-part biopic due here early next year, to Cleo, as in

Cleopatra

, queen of ancient Egypt. With

Catherine Zeta-Jones

tapped for the title role,

Hugh Jackman

as

Mark Antony

, and

Ray Winstone

as

Julius Caesar

, the film (believe it or not) is going to be a song-and-dance show, with words and music composed by indie band

Guided By Voices

.

"It's like an

Elvis

musical in a way," the director told MTV's movie blog. "It's not serious. I mean it's historically pretty accurate, but it's sort of like

Viva Las Vegas

meets

Tommy

."

Contact movie critic Steven Rea at 215-854-5629 or srea@phillynews.com.

Read his blog, "On Movies Online," at http://go.philly.com/onmovies.