IN 1984, some of the Western Hemisphere's leading populist singers gathered in Ecuador for a festival of nueva cancio'n, the Latin American "new song" movement. Gathered in the huge outdoor sports stadium were figures like Chile's Inti-Illimani, Cuba's Silvio Rodriguez, Mexico's Tania Libertad and the United States' Pete Seeger.

The show started at dusk, and taking the stage just before midnight was a performer that Seeger didn't recognize. The muscular, bearded fellow from Argentina carried an acoustic guitar and a harmonica rack, and when he began to sing, the 7,000 people in the audience rose to their feet and sang along. When his set ended, the crowd remained standing; they stomped and clapped and demanded encore after encore.

Seeger turned to some Latin Americans nearby and asked, Who is this guy? Leon Gieco, they replied. And how, Seeger asked, would you translate that song that everyone was singing just a few minutes ago?

"I only ask of God," they interpreted, "the ability to feel suffering."

Seeger was struck by the poetic Christianity of the lyrics, for this was no quiet sentimental folk song but a rousing rocker that had the crowd jumping around as if they were at a Bruce Springsteen show.

Seeger was so impressed by Gieco, in fact, that the elder statesman of North American folk music is introducing the "Bob Dylan of South America" via a joint tour that comes to Silver Spring's Blair High School this Friday.

The song that caught Seeger's attention in Ecuador is "Solo Le Pido a Dios" ("I Only Ask of God"). Gieco wrote it as a pacifist song in 1978, when it seemed that a border war between Chile and Argentina was imminent. Since then, though, the song has taken on a life of its own. With its prayer-like repetition and parable-like imagery ("I only ask of God that I am not indifferent to war, that big, powerful motor that smashes the innocents"), it has proven as adaptable for different situations as Seeger's "We Shall Overcome."

Joan Baez has sung the song in her European tours with Argentina's Mercedes Sosa, and Germany's Green Party has adopted "Solo Le Pido a Dios" for its demonstrations. In 1982, when the Falklands War and the problem of "the disappeared" had precipitated a crisis in Argentina, Gieco's song became an anthem for the opposition to the junta. When the junta forbade Gieco to sing the song, he would end his concerts by simply strumming the chords on his guitar. The crowd would then rise and sing the words for him.

Gieco didn't start out in the nueva cancion movement. On the commercial radio stations in Latin America, he explains, 80 percent of the music is Anglo-American rock 'n' roll in English. Gieco, now 38, grew up on the Beatles and he started his musical career playing rock nacional, Spanish-language rock 'n' roll. When he first traveled to the United States in 1982, though, and attended concerts by Bob Dylan, Joni Mitchell and the Grateful Dead, he realized he had misunderstood rock 'n' roll.

"I learned that rock 'n' roll is the folk music of the United States," he recalls. "The rock groups in Argentina were all copying something else, but I saw clearly that Dylan, Mitchell and the American rockers weren't copying anything. They were were making something very personal out of their own country's traditions.

"I asked myself what would happen if Paul McCartney sang a tango. Well, he would sing it well, because he has a good voice, but he could never sing it like Garvel, Argentina's 'King of the Tangos.' When Garvel sings a tango, you get goosebumps on your arms. I realized I was like Paul McCartney trying to sing a tango when I tried to sing North American rock 'n' roll," Gieco says.

So it was that Gieco embarked on a two-year musical odyssey. Traveling with a crew of musicians and filmmakers, Argentina's "King of Rock" traveled from the country's northern mountains to its southern islands, taping indigenous music on traditional instruments. The result was a television series and three best-selling record albums, all under the title of "De Ushaia a la Quiaca."

When Gieco returned to his own compositions, he drew on the Andean folk music of the mountains and the tango rhythms of the cities, much as Dylan had once drawn on the blues of the Delta and the ballads of the Appalachians.

LEON GIECO -- Appearing Friday with Pete Seeger at Montgomery Blair High School. Call 301/432-0200 or 301/270-9090.