The cause was complications of chronic obstructive pulmonary disease, his daughter Lian Amaris said.

A prolific author, Mr. Lester had more than four dozen books for adults and children to his credit. He was also variously a literary and cultural critic, folklorist, photographer, civil rights worker and professional musician.

As an essayist, he was a contributor to The New York Times Book Review, The Village Voice, Dissent and other publications. A resident of Belchertown, Mass., he was a retired faculty member of the University of Massachusetts, Amherst.

Mr. Lester's writing — he produced nonfiction and fiction — was largely devoted to portraying black American history, past and present. It was a history, his work made clear, that bound black lives together "like beads strung on a necklace of pain," as he wrote in The Times in 1976.

In the late '60s, during a period of acute tension between blacks and Jews in New York City, he caused a furor after he countenanced the reading of an anti-Semitic poem on a show he hosted on the radio station WBAI.Reviewers often praised his work for its vibrant immediacy, political urgency and deep rootedness in both black oral tradition and historical documents, including the narratives of former slaves.

Mr. Lester's best-known writing for adults includes the book "Look Out, Whitey! Black Power's Gon' Get Your Mama" (1968) and two volumes of memoir, "All Is Well" (1976) and "Lovesong: Becoming a Jew" (1988), about his conversion in 1982.

His children's books include "To Be a Slave" (1968), a nonfiction chronicle that was a Newbery Honor Book, as the finalists for the Newbery Medal, considered the Pulitzer Prize of children's literature, are known.

Mr. Lester also collaborated on a series of children's picture books with the distinguished African-American illustrator Jerry Pinkney. Among the most highly praised is "Sam and the Tigers" (1996), a retelling of the Victorian children's book "The Story of Little Black Sambo" purged of its myriad racist elements.

From the time he entered public life in the 1960s, Mr. Lester was periodically a lightning rod for controversies centering on race and religion.

In the late '70s, an essay he wrote for The Voice, which condemned some African-American leaders as anti-Semitic, caused him to be labeled anti-black.

In the late '80s, after Mr. Lester criticized the novelist James Baldwin for what he felt were anti-Semitic remarks, he was removed from the Afro-American studies department at the University of Massachusetts. The move engendered a national debate on censorship, political correctness and academic freedom.

Ultimately, Mr. Lester's personal, political and religious transformations lent a Cubist quality to his vision, allowing him to perceive myriad facets of American oppression simultaneously.

In an interview with The Los Angeles Times in 1992, he spoke of knowing both "the pain of a Jew when confronted with black anti-Semitism and the pain of a black when confronted with Jewish racism."

Over the years, as Mr. Lester's writings reflect, he also experienced serial immersions in black nationalism, Maoism, Roman Catholicism, mysticism and atheism.

His odyssey had taken him a long way from his early life in the Jim Crow South — an upbringing in which, Mr. Lester wrote long afterward, "childhood was a luxury."

A Jewish Ancestor

The son of Woodie Daniel Lester, a Methodist minister, and the former Julia Smith, Julius Bernard Lester was born in St. Louis on Jan. 27, 1939. When he was a child, the family moved to Kansas City, Kan., and later to Nashville.

"There were nothing but black kids in my class, the class across the hall, the school, the neighborhood," Mr. Lester, writing in 1976, recalled telling his incredulous young son. "I was 20 before I lived among whites."

Yet as a child, Mr. Lester learned that he had a Jewish ancestor on his mother's side, Adolph Altschul, an immigrant from Germany who had settled in Arkansas.

"My great-grandfather was a Jew, I say to myself," he later wrote, recalling that youthful epiphany. "I don't know what that means, not if meaning is confined to words and concepts."

But meaning, he continued, "is also feeling and sensation and wonder and questions."

Mr. Lester's father hoped he would follow him into the ministry, but the young Mr. Lester wanted only to become a folk singer. In the early 1960s, after earning a bachelor's degree in English from Fisk University, a historically black institution in Nashville, he moved to New York to pursue that calling.

There, he performed on the coffeehouse circuit as a singer and guitarist. He released two albums for Vanguard Records that melded folk and blues with his socially conscious lyrics: "Julius Lester" (1965) and "Departures" (1967).

Mr. Lester's first published book, which appeared in 1965, was an instructional manual, "The Folksinger's Guide to the 12-String Guitar as Played by Leadbelly,"written with Pete Seeger.

In the 1960s, Mr. Lester was closely involved as a writer and photographer with the Student Nonviolent Coordinating Committee, becoming the head of its photography department. In that capacity, he traveled to the South to document the civil rights movement and to North Vietnam to photograph the effects of American bombardment.

For much of this period he was an ardent separatist, arguing, as The Boston Globe reported in 1970, "that all effort should be turned to finding a way to establish a black nation within the territorial confines of the United States."

In "Look Out, Whitey!," his first book about race, Mr. Lester wrote: "The world of the black American is different from that of the white American. The difference comes not only from the segregation imposed on the black man, but from the very nature of blackness and its evolution under segregation."

Reviewing "Look Out, Whitey!" in The Times Book Review in 1968, the novelist and historian Truman Nelson called it "a magnificent example of the new black revolutionary writing that could generate the tidal force to sweep aside all the tired and dead matter on our literary shores."

In 1968, Mr. Lester became the host of a weekly show about political issues, broadcast on WBAI.

Late that year, Leslie R. Campbell, an African-American New York City schoolteacher, appeared as a guest on the show. The broadcast came on the heels of the racially charged controversy over local control of public schools in the Ocean Hill-Brownsville section of Brooklyn, a predominantly black neighborhood whose schools were staffed by a predominantly white cadre of teachers.

Amid the crisis, the United Federation of Teachers, many of whose members were Jewish, went on strike throughout the city, affecting hundreds of thousands of students and resulting in dozens of lost school days.

On Mr. Lester's show, on Dec. 26, 1968, Mr. Campbell read a poem written by one of his black teenage students. Dedicated to Albert Shanker, the president of the teachers' union, it began: "Hey, Jew boy, with that yarmulke on your head / You pale-faced Jew boy — I wish you were dead."

The poem, and Mr. Lester's on-air defense of it as an important evocation of a black student's experience, provoked a storm of complaint. The Anti-Defamation League of B'nai B'rith called publicly for Mr. Lester's dismissal from the station.

WBAI stood by Mr. Lester's right to have made the broadcast, as did the Federal Communications Commission, which reviewed the case in 1969. His show remained on the station until the mid-'70s.

Friction With Blacks

In what was widely viewed as an ideological about-face, Mr. Lester engendered controversy again in 1979 with public comments in support of American Jewry. That year, in an essay in The Voice, he castigated some black leaders as anti-Semitic for comments they had made in the wake of Andrew Young's resignation as the United States ambassador to the United Nations.

An African-American and a widely acknowledged hero of the civil rights movement, Mr. Young had resigned his post in August 1979 after meeting with a representative of the Palestine Liberation Organization — a move that many American Jews saw as a profound betrayal. As a result, some black leaders publicly blamed Jews for his resignation.

After his essay was published, Mr. Lester later wrote, an academic colleague asked him, "Don't you care what black people think of you?"

"I did," he wrote, "but not to the extent that I would give them power over my soul."

By then, Judaism, and the feeling and sensation and wonder and questions it occasioned, had begun to exert a pull on Mr. Lester. He had first felt that pull, he said, in the late 1970s, while preparing to teach a course on the intertwined history of blacks and Jews.

"I remembered books I'd read about Holocaust survivors," he wrote in a 1989 essay. "I was not that kind of survivor. The omnipresent threat of death on a Mississippi highway in 1964 was not Auschwitz. And yet, to live in an atmosphere where the presence of death is as palpable as the smell of honeysuckle lacerated the soul in ways one dared not stop to know."

In 1981, Mr. Lester said, he had a vision.

"In the vision, I was a Jew," he told NPR in 1995. "There was a yarmulke on my head, and I was dancing, and I was filled with incredible joy."

He converted the next year.

Although many critics praised "Lovesong," the chronicle of his conversion, the book exacerbated tensions between Mr. Lester and the Afro-American studies department at UMass. (He had joined the university's faculty in 1971.)

In his book, Mr. Lester criticized two widely venerated African-American figures: James Baldwin and, by extension, the Rev. Jesse L. Jackson.

Baldwin, who died in 1987 as Mr. Lester's book was going to press, had given a lecture at UMass a few years before in which he criticized the news media for reporting remarks that Mr. Jackson made during the 1984 presidential campaign. In those remarks, Mr. Jackson characterized New York City as "Hymietown."

Writing of Baldwin, Mr. Lester said, "I know he is not an anti-Semite, but his remarks in class were anti-Semitic, and he does not realize it."

In response — a development that received national attention — the Afro-American studies department forced Mr. Lester off its faculty in 1988, condemning him as "an anti-Negro Negro."

"It seems," Mr. Lester told The Los Angeles Times that year, with what can safely be described as knowing understatement, "that I challenge people."

Mr. Lester, who had won many awards for teaching during his time in the department, moved to the university's department of Judaic and Near Eastern studies. He retired from UMass in late 2003.

Mr. Lester's first two marriages ended in divorce. Besides his daughter Ms. Amaris, survivors include his wife, Milan Sabatini, whom he married in 1995; two sons, Malcolm and David; two other daughters, Jodie Lester and Elena Ritter; and eight grandchildren.

Among his other books for adults are "Revolutionary Notes" (1969), a collection of political and cultural essays, and the novel "The Autobiography of God" (2004), a mystical noir starring a young female rabbi.

His other children's books include "Day of Tears: A Novel in Dialogue," which won the American Library Association's Coretta Scott King Award in 2006.

From 1991 to 2001, he served as the lay religious leader of the Beth El Synagogue in St. Johnsbury, Vt.

In the 1980s, alight with his newfound faith, Mr. Lester went to Arkansas in search of Adolph Altschul, his great-grandfather. As he learned, Altschul's descendants, in an American odyssey of their own, had converted to Christianity.

When it came to that branch of the family, Mr. Lester discovered, he was its only surviving Jewish member.