Raising red, black and green flags and clenched fists, thousands of African American activists descended on the Mall yesterday, demanding reparations from the U.S. government for centuries of slavery and racism against black people.

Young and old traveled from nearly every corner of the country, but the assembly for Millions for Reparations was modest by Washington standards, as the rally filled a small swath of the grassy expanse near the U.S. Capitol.

But organizers called it an important moment for a largely grass-roots movement that has gained momentum over the last several years, with prominent lawyers and professors now calling for compensation to the descendants of slaves for free labor and decades of Jim Crow laws that they say are responsible for the economic and social ills in the black community today.

"This is the first time there has been a mass rally demanding reparations from the United States government," Conrad Worrill, chairman of the National Black United Front, told a spirited crowd. His group, which escorted dozens of Chicago residents on a 12-hour bus ride, was one of the chief organizers of the rally.

"They owe us!" Worrill added.

Throughout the afternoon, speakers from across the country spoke about the need for uniting the African American community behind the single banner of compensation and the need for lobbying lawmakers and others who have long been skeptical about the merits of reparations. Others spoke of the continued disparities in their neighborhoods and how reparations were needed to spark a new beginning for many communities of slave descendants.

With the U.S. Capitol as his backdrop, Rep. John Conyers Jr. (D-Mich.), who has introduced legislation in Congress for 13 years to create a commission to study reparations, urged people to contact their congressional representatives as soon as they arrived home.

"We will get [reparations] by contacting every single member of the House of Representatives, every single member of the Senate," he said, adding that blacks have been dealt a "historical injustice that can only be corrected" in Congress.

His challenge drew a wave of cheers from the chanting, sometimes swaying crowd of thousands that assembled at Third and Constitution from late morning to early evening. Before the line of speakers came to the platform, groups spread across the Mall, arguing how reparations should be administered. There seemed to be a soapbox every few feet.

"We built this country from the ground up," Willie Francona, who came from Philadelphia with his two daughters and son, said to those at his table filled with pamphlets and books. Pointing to the U.S. Capitol, he added: "That was our labor. And not a dime was given to any of the ancestors who sweat."

Such comments resonated throughout the hot summer day, and nearly half the crowd took to the shade along the edges of the Mall rather than brave the heat in front of the stage.

Many lay out on kente cloth and African print blankets and lawn chairs.

Manotti Jenkins of Chicago heard about the march on the Internet and flew to Washington with his wife and two daughters, ages 6 years and 6 months.

"Regardless of how much money I make as a corporate attorney, the impact of slavery is still here," he said. "We don't have the dignity and the respect we deserve as humans."

The rally got its most energetic jolt just before 2 p.m. when Minister Louis Farrakhan, head of the Nation of Islam, gave a short speech on the need to use the money responsibly, if reparations are ever approved.

"We cannot settle for some little jive token," he told the crowd. "We need millions of acres of land that black people can build."

Although police and rally organizers gave no official estimates, some acknowledged that the turnout was low compared with other events on the Mall. But supporters said the reparations movement was gaining. They cited lawsuits filed in federal courts in New York and New Jersey against companies that allegedly profited from the slave trade and a lawsuit planned against the federal government. Some civil rights organizations have yet to take a formal position on reparations, but the NAACP has called for a federal study on the issue.

"A fire has been started here today by a grass-roots movement, and that's the real victory of today," said Benjamin Chavis Muhammad, a leader in the Nation of Islam and a former head of the NAACP.

Critics of reparations contend that payments, whether to individuals or institutions, would present a logistical nightmare, and they question who should pay the money and who should receive it.

"I think it's bad politics and that the African American community would be better served trying to reach out to other groups," Glenn Loury, a Boston University sociology professor and critic of the reparations movement, said in an interview.

Some passersby also were skeptical. "The biggest problem, for example, is recent immigrants from, say, the Philippines," said Guy Tillinghast, 44, a doctor from Abingdon, Va. "Should their tax dollars go to pay for something 150 years before they came to this country?"

Many who attended the rally said they are passionate about the movement but realistic about its chances. "My great-great-grandmother was a slave in Florida, but I don't expect we're going to get any cash," said Suzanne Andersen, 51, a nurse from West Hempstead, N.Y. "What we need now is a foothold. We're still at the bottom. We've got millions of people in the prison system, and they all look like me."

For those who have fought for reparations for years, the day symbolized a movement coming of age. Ray Jenkins, a Detroit activist known as Reparations Ray, embraced the cause in the 1960s and has since been hailed as a pioneer of the reparations movement.

"They laughed at me when I talked about reparations all those years ago," he said after appearing on stage with Conyers. "But people aren't laughing anymore."

Staff writer Ian Shapira contributed to this report.

During the demonstration on the Mall, Sha'Kat Assata of Florida waves a towel emblazoned with "Free the Land."