These facts were taken from this trivia page.
British director John Schlesinger declined an offer to direct as he felt the story of Watergate should be told by an American.
The two lead actors memorized each other’s lines so that they could both interrupt each other in character. This unsettled a lot of the actors they were playing opposite, leading to a greater sense of verisimilitude.
When Woodward and Bernstein are discussing how to go about getting the bookkeeper to tell all, at Bernstein’s apartment, Bernstein grabs a cookie from a jar and throws it to Woodward. Bernstein’s own cookie is in his right hand but then turns into a cigarette, then a cookie again, then nothing, then a cookie, then a cigarette…
To prepare for their roles, Robert Redford and Dustin Hoffman hung out in the Washington Post newsroom for several weeks, observing reporters and attending staff meetings. Once, when Redford was standing in a hallway, a group of high school students came through on a tour of the newspaper offices. The students immediately started taking pictures of Redford with their pocket cameras. At that point, Bob Woodward walked by. Redford told the students, “Wait a minute! Here’s the real Bob Woodward, the guy I’m playing in the movie! Don’t you want to take a picture of him?” The students said no, and walked on. Hoffman also recalled that he had been asked by the Post’s science reporter to fetch a new typewriter ribbon. Due to Hoffman’s long hair and casual dress, the science reporter had mistaken him for a copy boy.
Frank Wills, the security guard who discovered the break-in at the Watergate complex, plays himself.
Robert Redford was in contact with Woodward and Bernstein before their book had been written, and encouraged them to write more about how they conducted their investigation and less about the events they were reporting. (Vanity Fair article, 04/2011.)
The interior Washington Post newsroom set was built on a stage at Warner Brothers Studio, in Burbank, California. The film’s production designer George Jenkins’ was a former New York Broadway scenic designer. Designing the newsroom based upon the actual newspaper’s newsroom, George’s plan layout utilizes false perspective in the rear set area to increase the depth and scale-size for camera. As the newsroom desks recede, the construction coordinator’s prop makers cut each prop desk down in size to fill in, and match the reduced scale for each line of desks. Shelving was also reduced in size. When filming the set’s front action area, the extra actors filling in the background set’s scale, were selected related to their height fulfilling the perspective scale set dressing relationship. Viewing the film, the false perspective of the studio set accomplishes the size and scale of the actual Washington Post Newsroom.
One scene involving Robert Redford on the phone is done in a continuous six-minute single take with the camera tracking in slowly. Towards the end Redford makes a mistake – he calls the phone caller by the wrong name – but as he stays in character it simply appears genuine and this was the take used in the final cut.
The telephone number that Robert Redford dials for the White House is the real number of the White House Switchboard: 456-1414.