Jack Valenti, a onetime confidant of President Johnson who spent nearly four decades as Hollywood’s chief Washington lobbyist and helped devise the “G” to “X” movie-rating system, died yesterday at his home in Washington of complications from a stroke in March. He was 85.

As president of the Motion Picture Association of America from 1966 to 2004, Valenti represented such powerful studios as Disney, Sony, Warner Bros., Paramount, MGM, 20th Century Fox, and Universal as well as several leading independent producers. Earlier, he established political connections as a Texas advertising and public relations executive that led to his strong ties to Johnson.

With an instinctive showman’s flair — notably his grandiloquent speaking style and access to movie stars — Valenti became the dominant powerbroker connecting Capitol Hill and the film colony. Besides his work on the ratings system in the late 1960s, he helped open up world markets for American-made films and secured passage of copyright legislation to protect movies into the digital age, which led to the proliferation of DVDs.

He also was a major gateway to Hollywood’s financial largesse during the campaign season. On any given week, Valenti met with actors, world leaders, and newspaper editors and was regarded as a brilliant and aggressive wielder of his glamorous pulpit.

Harry C. McPherson Jr., also a Johnson intimate who became a Washington lobbyist, called Valenti “an extremely successful advocate of the movie industry. You’d be hard pressed to find any lobbyist for any industry who did a more successful job than Valenti. I can’t think of many times when Jack Valenti lost.

“He had a lot to work with,” added Mr. McPherson, an occasional lobbying adversary of Valenti’s. “When senator X would want to go to Hollywood and would want some people to attend his fundraiser at the home of [former Walt Disney CEO] Michael Eisner or some producer or studio chief, he’d talk to Jack. Jack would set it up and very often go out there.”

A former Washington representative for Paramount, Lawrence Levinson, told the New Yorker magazine in 2001: “Jack was able to use the power and glamour and mystique of Hollywood. A new president came in, and [Valenti would] put himself in the center of the process of getting movies to the president. He’d get so excited. He’d call Sid Sheinberg ” — the president of MCA/Universal — “and say, ‘Sid! The president is going to Camp David! We’ve got to get him “Jaws”!'”

Valenti was widely considered an effective promoter for Hollywood on matters including censorship, videotape technology, copyright infringement and, in recent years, video and online “piracy” of trademarked films.