Jerry Rubin, the flamboyant 1960's radical who once preached distrust of "anyone over 30," died on Monday night in a Los Angeles hospital where he was being treated after having been struck by a car two weeks earlier. He was 56 and lived in the Brentwood section of Los Angeles.

A hospital spokesman said the cause was cardiac arrest, but Mr. Rubin had been unconscious and in critical condition since he was hit on the night of Nov. 14 while jaywalking across Wilshire Boulevard in the Westwood section of Los Angeles. His former wife, Mimi Leonard Fleischman, said that he had suffered multiple injuries.

As a bearded standard-bearer of the 1960's counterculture and opposition to the Vietnam War, Mr. Rubin carved himself a niche in the history of American radicalism with his energetic and sometimes comic gestures. He was among the founders of the Youth International Party, the Yippies, a militant but loose-knit group with a penchant for political theater. He appeared before a Congressional committee wearing a Revolutionary War costume, and was a center of attention at anti-war demonstrations in his Uncle Sam hat.

Mr. Rubin was prominent in the riotous protests at the 1968 Democratic National Convention in Chicago, which led to the famously unruly trial, in 1969 and 1970, of him and six other radical defendants -- the group known as the Chicago Seven. At the trial he showed up wearing judge's robes covering a blue Chicago police shirt.

After the 1960's, Mr. Rubin wrote, lectured, sought self-improvement and then worked in New York on Wall Street and as an entrepreneur. In the 1980's, he became known for his promotion of "networking," bringing together ambitious young professionals at parties at the Palladium nightclub in Manhattan. Transformed from protester to businessman but still demonstrating a flair for the public gesture, he held a series of public "Yippie vs. Yuppie" debates with Abbie Hoffman, another former leader of the Yippies, who committed suicide in 1989.

Looking back years later at the 1960's, Mr. Rubin called himself one of "the anti-capitalistic comics of the 1960's" who used street theater to pursue, without much success, "the radical dream of transforming the system from outside."

He once campaigned to elect a pig as President the United States, and in 1967 he dropped dollar bills onto the floor of the New York Stock Exchange.

Though he later renounced his anti-capitalism, he defended his fervent opposition to the Vietnam War. "Our nationwide campaign to build public opposition to the Vietnam War succeeded, and the war ended," he wrote in an article in 1990.

The Chicago Seven trial produced some of the most bizarre courtroom scenes in American jurisprudence. Mr. Rubin and other defendants -- Mr. Hoffman, Tom Hayden, Rennie Davis, David Dellinger, John Froines and Lee Weiner -- all charged with conspiracy to disrupt the Democratic convention, taunted the iron-willed judge, Julius J. Hoffman. The judge ordered an eighth defendant, Bobby Seale, tried separately because he was so disruptive.

During the trial, which was in Federal District Court, Judge Hoffman aimed sarcastic remarks and occasional tirades at the defendants and their lawyers, including William Kunstler. The defendants chewed jelly beans at first and later screamed insults at the prosecutors and the judge, whom Mr. Rubin denounced as "the laughingstock of the world."

Mr. Rubin and his co-defendants were acquitted of conspiracy, but he and four of the others were found guilty of incitement. Those convictions were overturned by an appeals court, which cited, among other reasons, what it called Judge Hoffman's "antagonistic" courtroom demeanor.

After the Chicago Seven trial, a best-selling autobiography by Mr. Rubin came out. Then he went through a difficult period in the early 1970's, when his "life came crashing down around him," as one reviewer of his writing, the television performer Orson Bean, wrote later, after "a group of young kids publicly retired him for being over 30" and his political movement disappeared.

After that, Mr. Rubin began what was to become a prolonged round of self-improvement, which he was heard to call "a smorgasbord course in New Consciousness." He tried EST, meditation, modern dance, massage, acupuncture and hypnotism. As the 1970's went on, he lectured and did more writing.

In 1978, Mr. Rubin, a son of a Cincinnati truck driver who became an official in the teamsters' union, married Mimi Leonard, a former debutante who worked for ABC-TV in New York. They lived in a posh apartment on the Upper East Side of Manhattan.

With the passage of time, Mr. Rubin became "a buttoned-down entrepreneur for the 1980's," as one cultural critic put it. A watershed of sorts came in 1980, when he wrote that while he still had "many of the same criticisms and same values" as in the 1960's, he had learned "that the individual who signs the check has the ultimate power."

"I know that I can be more effective today wearing a suit and tie and working on Wall Street than I can be dancing outside the walls of power," he said.

Indeed, he worked briefly for the Wall Street firm of John Muir & Company and went on to make a new name for himself promoting networking.

By 1985, Mr. Rubin's soirees at the Palladium on East 14th Street were bringing together thousands of networkers. "I don't like to use the word, but every Yuppie in New York comes," he told an interviewer.

In 1991 he moved to Los Angeles, where his business activities included marketing a nutritional drink named Wow! Forbes magazine reported in 1992 that Mr. Rubin said he was making $60,000 a month as a distributor for Omnitrition International, a Texas company that sold powdered mixes for Wow! and other beverages.

Mr. Rubin was born on July 14, 1938 -- Bastille Day, as he liked to say -- in Cincinnati. He attended Oberlin College, worked as a reporter and editor at The Cincinnati Post and studied further at the University of Cincinnati, Hebrew University in Jerusalem and, briefly, the University of California at Berkeley.

His marriage ended in divorce in 1992.

Mr. Rubin is survived by a daughter, Juliet Clifton Rubin, and a son, Adam Winship Rubin, both of Beverly Hills, and by a brother, Gil, of Trumbull, Conn.

The funeral is to be at 10 A.M. on Thursday at Hillside Memorial Park in Los Angeles.

Photo: Jerry Rubin went from radical to businessman during a colorful life. (Reuters/Bettmann, 1968; Associated Press, 1989)

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