WASHINGTON — Tens of thousands of people marched to the Martin Luther King Jr. Memorial and down the National Mall on Saturday, commemorating the 50th anniversary of King’s famous speech and pledging that his dream includes equality for gays, Latinos, the poor and the disabled.

The event was an homage to a generation of activists who endured fire hoses, police abuse and indignities to demand equality for African-Americans. But there was a strong theme of unfinished business.

“This is not the time for nostalgic commemoration,” said Martin Luther King III, the oldest son of the slain civil rights leader. “Nor is this the time for self-congratulatory celebration. The task is not done. The journey is not complete. We can and we must do more.”

Eric Holder, the nation’s first black attorney general, said he would not be in office, nor would Barack Obama be president, without those who marched.

“They marched in spite of animosity, oppression and brutality because they believed in the greatness of what this nation could become and despaired of the founding promises not kept,” Holder said.

Holder mentioned gays, Latinos, women and the disabled as those who had yet to fully realize the Rev. Martin Luther King Jr.’s dream. Others in the crowd advocated organized labor, voting rights, revamping immigration policies and access to local post offices.

Rep. John Lewis, D-Ga., the only surviving speaker from the 1963 March on Washington, railed against a recent Supreme Court decision that effectively erased a key anti-discrimination provision of the Voting Rights Act. Lewis was a leader of a 1965 march, where police beat and gassed marchers who demanded access to voting booths.

“I gave a little blood on that bridge in Selma, Ala., for the right to vote,” he said. “I am not going to stand by and let the Supreme Court take the right to vote away from us. You cannot stand by. You cannot sit down. You’ve got to stand up. Speak up, speak out and get in the way.”

Organizers expected about 100,000 people to participate in the event, the precursor to the actual anniversary of the Aug. 28, 1963, march that drew some 250,000 to the National Mall and ushered in the idea of massive, nonviolent demonstrations.

Marchers began arriving early Saturday, many staking out their spots as the sun rose in a clear sky over the Capitol. By midday, tens of thousands had gathered on the National Mall.

Lynda Chambers, 58, gave up a day’s pay to attend because her retail job does not provide paid vacation. Even as a 7-year-old at the time of the original march, she felt alienated and deprived of her rights. Remembering those feelings, she said, she was compelled to make the trip Saturday.

“I wanted to have some sort of connection to what I have always known, as far as being a black person,” she said.

Speakers frequently mentioned persistent high unemployment among blacks, which is about twice that of white Americans, and the acquittal of George Zimmerman for the shooting death of unarmed black teenager Trayvon Martin in Florida. Along the Mall, Martin’s picture was nearly as ubiquitous as King’s.

Nancy Norman of Seattle said she was disappointed more people who look like her had not attended. She is white. But the 58-year-old said she was glad to hear climate change discussed alongside voting rights.

“I’m the kind of person who thinks all of those things are interconnected. Climate change is at the top of my list,” Norman said. “I don’t think it’s one we can set aside for any other discussion.”