The cause was complications of Alzheimer’s disease, his son Frederic said.

Mr. Silber, an ardent leftist, found common cause with Woody Guthrie, Pete Seeger, Lee Hays and others who regarded folk music as a form of political protest and a way of affirming the dignity of working people. In 1946, with other supporters, they founded People’s Songs Inc., which published a bulletin “to create, promote and distribute songs of labor and the American people.” Mr. Silber became its executive secretary in 1947.

After People’s Songs went under in 1949, having exhausted its meager funds on Henry Wallace’s failed 1948 presidential campaign, Mr. Silber, Mr. Seeger and others founded Sing Out!

Mr. Silber borrowed the title from the third verse of “The Hammer Song” (later known as “If I Had a Hammer), written in 1949 by Mr. Seeger and Mr. Hays, with its refrain “I’d sing out danger, I’d sing out a warning, I’d sing out love between all my brothers (and my sisters) all over this land.”

The song appeared on the cover of the first issue, which came out in May 1950.

Mr. Silber assumed the title of editor within a few issues and continued in that post until 1967, steering the magazine through a heady period in which a growing audience embraced Southern blues singers, guitar and banjo pickers from the Appalachians and a new generation of young protest singers like Joan Baez and Mr. Dylan.

Under Mr. Silber, the magazine printed, for the first time, “Sixteen Tons,” “This Land Is Your Land,” “Michael Row the Boat Ashore,” “Bells of Rhymney” and “Cotton Fields.”

“He was one of a handful of people who can be called the architects of the folk revival, other than the performers themselves, and he helped move the music forward,” said Mark D. Moss, the current editor of Sing Out! “A lot of people thought of folk music as a white guy writing his own songs and playing guitar, but Irwin went deeper, presenting songs from different cultures in different languages. He always saw this as an empowering, people-up movement.”

Mr. Silber, who wrote a monthly column called “Fan the Flames,” kept the pages lively. In an open letter to Mr. Dylan in November 1964, he accused him of becoming a sellout more interested in his own image and the entourage around him than in his audiences.

“I saw at Newport how you had somehow lost contact with people,” he wrote, referring to that year’s Newport Folk Festival. “It seemed to me that some of the paraphernalia of fame were getting in your way.”

Even worse, Mr. Silber argued, Mr. Dylan had turned away from the political protest songs that first brought him fame. “Your new songs seem to be all inner-directed now, inner-probing, self-conscious — maybe even a little maudlin or a little cruel on occasion. And it’s happening onstage, too. You seem to be relating to a handful of cronies behind the scenes now — rather than to the rest of us out front.”

Mr. Dylan was not amused. Mr. Silber is often proposed as a possible target of the Dylan song “Positively Fourth Street.”

One line in that song goes: “You say I let you down. You know it’s not like that./If you’re so hurt, why then don’t you show it?”

Irwin Silber was born on Oct. 17, 1925, in Manhattan, where he attended Seward Park High School. Politically active from an early age, he joined the Young Communist League, the American Student Union and American Youth for Democracy while still in his teens.

At Brooklyn College he formed the American Folksay Group, a politically minded folk-music and folk-dancing organization. After graduating in 1945 with a bachelor’s degree in English, he developed a close relationship with the musicians and folklorists, like Alan Lomax, who were involved in presenting and preserving folk music.

He would later be brought before the House Un-American Activities Committee for questioning, but he managed to deflate the atmosphere of high drama. On being asked what subject he had taught at the Communist-sponsored Jefferson School of Social Science, he answered, truthfully, “Square dancing.” He left the Communist Party in the late 1950s.

After leaving Sing Out!, Mr. Silber wrote for Guardian, a radical weekly. He became its editor in 1972 but left in 1978 after doctrinal disputes divided the staff members.

Mr. Irwin’s first two marriages ended in divorce. In addition to his son Frederic, of Redmond, Wash., he is survived by his wife, the singer Barbara Dane; another son, Joshua, of Manhattan; a daughter, Nina Silber-Hutchins, of Needham, Mass.; two grandchildren; two stepsons, Jesse Cahn of Luther, Okla., and Pablo Menendez of Havana; a stepdaughter, Nina Menendez of Oakland, Calif.; two step-grandchildren; and one step-great-grandchild.

Besides editing Sing Out!, Mr. Silber recorded protest songs from liberation movements around the world on the Paredon label, which he and Ms. Dane founded in 1970 and ran until the early 1980s.

He published many important folk-song collections, notably “Songs of the Civil War” (1960), “The Great Atlantic and Pacific Song Book” (1965), “Songs of the Great American West” (1967) and, with Fred Silber, “Folksinger’s Wordbook.” He also wrote “Press Box Red” (2003), a biography of Lester Rodney, the sports editor of The Daily Worker.