WILD APPLAUSESing Your Song: Documentary by Susanne Rostock. 10 p.m. Mon. on HBO.

The title of Susanne Rostock's documentary on the life of Harry Belafonte comes from something Paul Robeson said to Belafonte once in a New York theater where the young Harlem-born singer and then-budding social activist was starring in a play. "Get them to sing your song and they will want to know who you are," Robeson said.

"Sing Your Song," airing Monday night on HBO, is filled with the names of giants - Martin Luther King Jr., Robert and John Kennedy, Eleanor Roosevelt, Nelson Mandela - all men and women with whom Belafonte has walked and worked during a lifetime of battling injustice. He made his name as a singer and then used his talent, as well as his undeniable sex appeal, to draw attention to various causes through the years, including the civil rights struggles of the '60s, the end of apartheid in South Africa, and extreme hunger and poverty in Africa in recent years.

Belafonte speaks frequently during the 100-minute film, which was produced in part by his daughter Gina. When he does, he sounds as if he were giving a speech. Having seen him speak to a roomful of critics and reporters during the summer, I can report that what you hear in the film is what you get in person: a man whose commitment to social justice is so passionate, only oratory will do to express what he feels.

Belafonte was born in Harlem, but spent much of his childhood in his mother's native Jamaica, where he first heard the music he would later popularize in the United States. Returning to Harlem at the outbreak of World War II, he found it ironically difficult to adapt to life in his native land. After a stint in the Navy, he returned to New York and held a few menial jobs.

By chance, he was able to see a production of the American Negro Theatre in Harlem, and his professional course was set. He joined the company and later studied at the New School for Social Research with other young actors such as Marlon Brando and Walter Matthau.

He also nurtured a budding singing career, first as a jazz singer, before striking gold by singing the calypso music he'd heard during his Jamaican childhood.

Rostock's film is only minimally a portrait of a singer and actor. The Tony Award is here, his stint as the first black TV producer for his own specials, directed by Norman Jewison, his roles in films such as "Carmen Jones" and "Island in the Sun," which caused an uproar because it suggested a romance between Belafonte's character and co-star Joan Fontaine.

But the bulk of the film is a portrait of the artist as a lifelong activist. The more he rose in show business, the more aware he became of discrimination and injustice. Touring with Marge and Gower Champion, his eyes were opened to the harsh reality of discrimination when they played Southern dates. And in Las Vegas, he wasn't allowed to stay at the hotel where he was performing.

In the '60s, Belafonte was reminded of how much work remained to be done on discrimination when, during a duet on TV, British singer Petula Clark placed her hand on his arm. The idea of a white woman touching a black man was scandalous.

Belafonte met King in the '50s and forged a deep friendship with the civil rights leader, who would often use Belafonte's apartment as a refuge from the public spotlight. Belafonte also met the Kennedys, who were hesitant at first to get involved in the civil rights battle. But King saw hope, particularly in the attorney general. Despite the fact that Robert Kennedy had been a staff lawyer for the Senate Permanent Committee for Investigations, a job secured by Sen. Joseph McCarthy, King believed there was something good in Kennedy, struggling to get out.

To some extent, the film glosses over issues in Belafonte's personal life, including his two failed marriages. He was always determined to be a good father, but his children quickly got used to the fact that not only was their dad going to be away performing much of the time, but he was also apt to be off to far-flung places to crusade for one cause or another.

Belafonte easily admits his personal shortcomings, but that doesn't mean he's about to change at this stage of his life, nor does anyone expect him to. It also doesn't mean he could have changed even when he was younger. His heart was always in the right places, plural, and that was the problem.

The portrait of Belafonte that emerges from the film is also the portrait of the times of his life, the times of the nation's life in the past 60 years. Listening to contributors such as Rep. John Lewis and the Rev. Willie Blue, who were also veterans of the civil rights movement in the South, and viewing the news footage of the demonstrations in Selma, Ala., and elsewhere, we may be tempted to believe we've come a long way.

You'd get an argument from Harry Belafonte if you suggested as much, however. Now, at 84, he walks with a cane, moving slowly, some might say, but still moving, still pushing forward. Whether it's going to Africa to fight famine or meeting with young gang members in Los Angeles to help them find their own way in life, Belafonte is still singing his own song and hoping others will join in.

E-mail David Wiegand at dwiegand@sfchronicle.com.