LOS ANGELES - Jack Valenti, the former White House aide and film-industry lobbyist who instituted the modern movie-ratings system and guided Hollywood from the censorship era to the digital age, died yesterday at age 85.

Valenti had a stroke in March and was hospitalized for several weeks at Johns Hopkins University Medical Center in Baltimore.

He died of complications from the stroke at his Washington, D.C., home, said Seth Oster of the Motion Picture Association of America.

"In a sometimes unreasonable business, Jack Valenti was a giant voice of reason," Steven Spielberg said in a statement. "He was the greatest ambassador Hollywood has ever known."

Valenti was a special assistant and confidant to President Lyndon Johnson when he was lured to Hollywood in 1966 by movie moguls Lew Wasserman and Arthur Krim.

When he took over as president of the Motion Picture Association of America, Valenti was caught between Hollywood's outdated system of self-censorship and the liberal cultural explosion taking place in America.

Valenti abolished the industry's restrictive Hays code, which prohibited explicit violence and frank treatment of sex, and in 1968 oversaw creation of today's letter-based ratings system.

"While I believe that every director, studio has the right to make the movies they want to make, everybody else has a right not to watch it," Valenti told the Associated Press shortly before his retirement in 2004. "All we do is give advance cautionary warnings and say this is what we think is in this movie."

Dan Glickman, his successor at the MPAA, said that Valenti embodied the "theatricality" of the industry.

"Jack was a showman, a gentleman, an orator and a passionate champion of this country, its movies, and the enduring freedoms that made both so important to this world," Glickman said.

Valenti's Washington career was born from tragedy. As a Texas-based political consultant working for then-Vice President Johnson, Valenti was riding in the presidential motorcade on Nov. 22, 1963, when President Kennedy was assassinated in Dallas. Valenti, six cars behind the president, initially didn't know what happened.

In a 2003 interview, he said that the assassination "is so seared in my memory I literally, sometimes at night - not often, but once or twice a year - I relive that day."

Oliver Stone's 1991 film "JFK" angered Valenti. Stressing he wasn't speaking for the MPAA, he said the film's implication that LBJ was involved in the assassination was "quackery" plucked from a "slag heap of loony theories."

Hurried aboard Air Force One for Johnson's historic flight back to Washington, Valenti was instantly drafted as a special assistant to the new president.

Yet Valenti resigned in 1966, over Johnson's objections, to accept the movie post. He became one of the highest-paid and best-known trade-association executives, with a salary topping $1 million and his own star on the Hollywood Walk of Fame.

He met his future wife, Mary Margaret Wiley, in 1955 through his friendship with Johnson, when LBJ was a U.S. senator from Texas. Wiley was LBJ's longtime secretary. She and Valenti had three children.

"I'm the luckiest guy in the world," he said in 2004, "because I spent my entire public working career in two of life's classic fascinations, politics and Hollywood. You can't beat that." *