Image caption British actor Dave Prowse played Darth Vader in the film

Star Wars sequel The Empire Strikes Back is to be preserved by the US Library of Congress as part of its National Film Registry.

Also included is Star Wars director George Lucas's student film Electronic Labyrinth: THX 1138 4EB, made in 1967.

Spike Lee's Malcolm X, about the black political revolutionary and Saturday Night Fever also make the list.

Each year, 25 "culturally" significant films are added to the registry, which was founded in 1989.

Lucas's Star Wars and American Graffiti are among the 550 titles already selected for preservation.

This year's raft of entries includes Robert Altman's 1971 western McCabe and Mrs. Miller starring Warren Beatty, Blake Edwards' The Pink Panther and Elia Kazan's first feature film, A Tree Grows in Brooklyn, made in 1945.

Horror blockbuster The Exorcist and Watergate thriller All the President's Men have also been named.

Under the terms of the National Film Preservation Act, the selected works are not the "best" American films but seen as works of enduring significance to US culture.

Films are suggested by the National Film Preservation Board and by the public - who nominated more than 2,100 films in 2010.

Librarian of Congress James H. Billington said: "The National Film Registry is a reminder to the nation that the preservation of our cinematic creativity must be a priority because about half of the films produced before 1950 and as much as 90% of those made before 1920 have been lost to future generations."