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Carl Oglesby, who led Students for a Democratic Society as it publicly opposed the Vietnam War but who was later expelled by a radical faction that became the Weather Underground, died on Tuesday at his home in Montclair, N.J. He was 76.

The cause was lung cancer, said his partner, Barbara Webster.

Mr. Oglesby, who left a military industry job and a comfortable lifestyle to join S.D.S., was the organization’s president from 1965 to 1966. Trained as an actor and a playwright, he was regarded as one of the most eloquent spokesmen of the period.

“He was the great orator of the white New Left,” Todd Gitlin, a Columbia University professor who was the president of S.D.S. from 1963 to 1964, said in a telephone interview on Tuesday. “His voice was a well-practiced instrument.”

Mr. Oglesby’s speech “Let Us Shape the Future,” delivered at an antiwar rally in Washington on Nov. 27, 1965, is considered a landmark of American political rhetoric. In it, he condemned the “corporate liberalism” — American economic interests disguised as anti-Communist benevolence — that, he argued, underpinned the Vietnam War.

Carl Oglesby in 1968. As a leader of Students for a Democratic Society, he helped galvanize opposition to the Vietnam War.CreditNeal Boenzi/The New York Times

“For all our official feeling for the millions who are enslaved to what we so self-righteously call the yoke of Communist tyranny,” Mr. Oglesby said that day, “we make no real effort at all to crack through the much more vicious right-wing tyrannies that our businessmen traffic with and our nation profits from every day.”

Yet unlike many of his compatriots on the left, Mr. Oglesby was, by his own account, a “radical centrist.” He proposed, for instance, that S.D.S. collaborate with the conservative group Young Americans for Freedom on antiwar demonstrations, a suggestion that only rankled the group’s more radical members.

Mr. Oglesby, who over the years taught courses on politics and on the mystical writings of Carlos Castaneda at Antioch College, Dartmouth and the Massachusetts Institute of Technology, wrote many books. They include a memoir, “Ravens in the Storm: A Personal History of the 1960s Antiwar Movement” (2008), and several volumes analyzing the assassination of President John F. Kennedy.

Carl Preston Oglesby Jr. was born on July 30, 1935, in Akron, Ohio, where his father worked in a tire plant. His parents were poor Southerners who had come North seeking opportunity; Carl Junior was the first in the family to hold a white-collar job.

He studied at Kent State University before dropping out to pursue acting and playwriting in New York. Returning to the Midwest, he took a bachelor’s degree at the University of Michigan.

By the mid-1960s, Mr. Oglesby was working in Ann Arbor, Mich., as a technical writer for the Bendix Corporation, an electronics concern involved in military work. He had a wife, three children and a red Alfa Romeo.

During this time, a paper he wrote advocating the immediate withdrawal of American forces from Vietnam was published, along with one of his plays, in the University of Michigan’s literary magazine. As a result, Mr. Oglesby was recruited into S.D.S.

He soon quit his job and sold his house and car and within a year was elected president of the group, which had about 2,000 members. Under Mr. Oglesby’s stewardship, S.D.S. helped galvanize public opposition to the war; by 1968, its membership had grown to about 100,000.

In 1969, with the group’s radical-left faction in ascendance, Mr. Oglesby was expelled after an S.D.S. tribunal pronounced him insufficiently Marxist and more than sufficiently bourgeois.

S.D.S. dissolved that year. It was supplanted by the Weathermen, later called the Weather Underground, which advocated the violent overthrow of the United States government.

Mr. Oglesby’s marriages, to Beth Rimanoczy, Anne Mueller and Sally Waters, ended in divorce. Besides his partner, Ms. Webster, he is survived by two daughters, Aron DiBacco and Shay Oglesby-Smith, and a son, Caleb, all from his first marriage; and five grandchildren.

His other books include “Bob Vila’s Guide to Buying Your Dream House” (1990), written with Mr. Vila; and “The New Left Reader” (1969), which he edited.

Mr. Oglesby also recorded two albums of original folk music.

If he seemed at loose ends after his expulsion from S.D.S., there was reason, Mr. Gitlin said.

“He bet the ranch on the movement,” he said. “He transplanted his world, radically. I think part of his power as an orator was that you could sense that he was bringing his whole self into this. He was at stake. It wasn’t a role; it was a life.”