It was a scalding, polarizing moment in the civil rights struggle: Two black American sprinters--draped with medals at the 1968 Mexico City Olympics--thrust black-gloved fists into the air during their national anthem. It was a gesture that signified either noble defiance or overt sedition, depending on your point of view and, probably, color.

Tommie Smith had just shattered the world record in the 200 meters to win the gold. Fellow American John Carlos finished third, grabbing the bronze. It was their turn to climb the platform and accept the just rewards of their years of training. But unlike so many events in sports, this was not a moment that could exist in a vacuum. This was 1968, the year that everything blew up.

HBO tells the story of the men who raised rebellious fists, and of the complex personal and political motivations that fueled them, in "Fists of Freedom: The Story of the '68 Summer Games," a compelling and intricately drawn one-hour documentary airing tonight at 10.

It was October, and the horrible year was finally drawing to a close. Smith, Carlos and fellow sprinter Lee Evans were students at San Jose State University--renowned among colleges as "Speed City," the home of America's fastest runners--and were insulated from much of the strife. That is, until a militant young black professor named Harry Edwards began speaking out and launched the three sprinters--who were Olympic shoo-ins--on a course to become cultural symbols.

"Sports was a legitimate lever to bring about changes relative to race," Edwards says in the documentary. Now 56, he is a sociology professor at the University of California at Berkeley.

Edwards urged black athletes to join the civil rights struggle in dramatic fashion by boycotting the 1968 Olympics. The dissension rocked the monolithic Olympic lords--the documentary savages International Olympic Committee President Avery Brundage as a racist patrician who repeatedly refers to Smith, Carlos and Evans as "boys."

But the documentary effectively shows the lack of solidarity among black athletes as well. Even though most had experienced racism, they had never been asked to be political. Some chose to abstain.

"I just tuned it out," says Bob Beamon, who set a long-jump record during that Olympics that stood until 1991. "It was too much sacrifice."

Some athletes sat out of the movement. Some jumped in with both feet. Others found a middle ground. All struggled.

"I couldn't be altogether revolutionary because that would close the door for other guys behind me," says Charlie Scott, who was on the 1968 U.S. basketball team.

The boycott failed, but the embers of protest burned on. When Smith and Carlos got their moment in the spotlight on the podium, they did not hold back. They raised their fists "to God," says Smith, 55.

"It was a cry for solidarity by my fellow brothers and sisters in this country who had been lynched, who had been shot, who had been bitten by dogs, who had had water hoses turned on them," says Smith, a former ROTC student. "It was a cry for freedom." Carlos declined to be interviewed for the documentary.

Next it was Evans's turn. He won the gold in the 400 meters in world record time. On the medal stand, during the national anthem, he staged his protest by wearing a black beret--at the time, a symbol of the revolutionary Black Panthers. But he made a crucial mistake: He smiled.

When he returned home, he was besieged by black activists who chastised him for grinning on the podium, saying it made light of the struggle. But Evans had another concern: He had received racist hate mail before the Games, telling him he would be shot on the medal stand.

"I thought maybe they can't shoot a guy who's smiling," says Evans, 52.

There was more ugliness: The legendary Jesse Owens--who shattered Adolf Hitler's notions of black racial inferiority at the 1936 Berlin Olympics--was brought in by the Olympic Committee to "tame" the black athletes. But they hounded him as "Uncle Jesse," a tool of the white establishment. He reacted with confusion and pain.

Such are the documentary's strong points. One glaring weakness is the role--whatever it may have been--of black female athletes. They are written off in a single sentence: "Black women, whose opinion had been regretfully ignored by the men, won three gold medals."

Implicitly, that means the black female athletes were doubly oppressed: by the white majority and by black men.

Edwards himself comes in for criticism from some of the athletes, who call him an "opportunist" who should have come to Mexico City to stand along with them.

That such an extraordinary assemblage of athletes managed to perform so superbly against a backdrop of racial strife is impressive. That the nation survived 1968 is perhaps more impressive.

CAPTION: Olympic medalists Tommie Smith and John Carlos raise their fists in the black power salute at the 1968 Games.