Mercedes Sosa, at 74; Argentine singer championed social justice in South America

With a rich contralto voice, Ms. Sosa was foremost a compelling singer whose career spanned five decades. She performed with entertainers as varied as rock star Sting, the Cuban singer-songwriter Pablo Milanes, and folk singer Joan Baez, who said she was so moved by Ms. Sosa’s “tremendous charisma’’ and emotive firepower that she once dropped to her knees and kissed her feet.

Ms. Sosa’s towering artistry, which led to several Latin Grammy Awards, belied her physical dimensions. Short, round, dark-skinned, and often dressed in peasant clothing, Ms. Sosa was affectionately nicknamed “La Negra,’’ the Black One, as an homage to her indigenous ancestry.

It was a term of endearment that followed her throughout the Spanish-speaking world, said music scholar Jonathan Ritter, who has written about Ms. Sosa. “It’s hard to overestimate her popularity and importance as a standard-bearer of folk music and political engagement through folk music,’’ he said.

Ms. Sosa once declared that “artists are not political leaders. The only power they have is to draw people into the theater.’’ While not defining herself as a political activist, Ms. Sosa asserted herself in the nueva canción musical movement of the 1960s and 1970s that blended traditional folk rhythms with politically charged lyrics about the poor and disenfranchised.

This “new song’’ movement, formed by singers, poets, and songwriters with Marxist leanings, cast light on the struggle against government brutality and the plight of the downtrodden throughout the hemisphere. Ritter said many of the nueva canción songs favored by Ms. Sosa “drew upon the rich heritage of Latin American poetry and literature to score their political messages.’’ This, he said, gave it a far more enduring fascination than protest songs in the United States during that period, whose “blunt, direct lyrics were part of their political efficacy, but also limited their long-term poetic appeal.’’

Ms. Sosa came under official harassment and intimidation by the right-wing, nationalist junta that ruled Argentina from 1976 to 1983. The government was responsible for the deaths and disappearances of an estimated 30,000 real and perceived leftists, and Ms. Sosa transformed her sold-out concerts into rallies against the abuses of power.

Her songs were banned from Argentine radio and television, and she courted arrest by singing anthems of agrarian reform, such as “When They Have the Land’’ at one performance in the university city of La Plata. Many in attendance were arrested by security forces, and Ms. Sosa was publicly humiliated by an officer who walked onstage and conducted a body search.

She scheduled more concerts in the face of threats against her. They were subsequently canceled when anonymous bomb threats were called in. The military governor of Buenos Aires prohibited her from further performances. Unable to earn a living or speak out as an opponent of the regime, she moved in exile to Europe in 1979 and lived for three years in France and Spain.

She recalled this as a dark period for her artistically, and at times her voice failed. “It was a mental problem, a problem of morale,’’ she told The New York Times. “It wasn’t my throat, or anything physical. When you are in exile, you take your suitcase, but there are things that don’t fit. There are things in your mind, like colors and smells and childhood attitudes, and there is also the pain and the death you saw. You shouldn’t deny those things, because to do so can make you ill.’’

Ms. Sosa returned to Argentina shortly before the dictatorship crumbled, and she found that her popularity had risen to a dramatic new peak. At home, her concerts attracted tens of thousands of ticket buyers, and her albums sold hundreds of thousands of copies.

Abroad, she was a star attraction as well, and a political celebrity. She received a 10-minute standing ovation for a 1987 concert at Carnegie Hall and received ecstatic reviews when appearing in other major American cities. She broadened her repertoire to include rock, pop, and cabaret songs, always sung in her native language.

Esquire magazine noted, “Your Spanish may or may not be good, but Mercedes Sosa requires no translation. Hers is the song of all those who have overcome their fear of singing out.’’