WASHINGTON Mercedes Sosa, an Argentine singer who emerged as an electrifying voice of conscience throughout Latin America for songs that championed social justice in the face of government repression, died Sunday at a medical clinic in Buenos Aires. She was 74, and had liver, kidney and heart ailments.

With a rich contralto voice, 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 Sosas tremendous charisma and emotive firepower that she once dropped to her knees and kissed Sosas feet.

Sosas towering artistry, which led to several Latin Grammy Awards, belied her physical dimensions. Short, round, dark-skinned and often dressed in peasant clothing, 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 ethnomusicologist Jonathan Rit- ter, who has written about Sosa. Its hard to overestimate her popularity and importance as a standard-bearer of folk music and political engagement through folk music, he said.

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, Sosa asserted herself in the nueva cancion 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.

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.