ATLANTA (CNN) -- Sen. Barack Obama (D-IL) invoked the names of civil rights leaders and criticized the war in Iraq at a political rally Saturday in Atlanta.

"When ordinary people have stood up, extraordinary things have happened." the Democratic presidential candidate declared before an audience of more than 10,000 assembled on the Georgia Tech campus.

The Illinois senator told the audience that the Rev. Martin Luther King, Jr. had described the Vietnam War as "morally untenable" in comments he made not far from the site of this rally. And Obama said that while parallels between Vietnam and Iraq were not precise, he added, "We don't engage in war because it's a sport."

He received some of his loudest applause discussing the war, saying "It's time for us to start bringing our combat troops home. We don't want to see Iraq completely collapse into bloodshed."

He added, "We've got national security concerns that we've got to tend to, but we are not going to solve the problem by sending another hundred billion dollars every year, and sending thousands of more troops to come back injured. There's no military solution to the problems that we have in Iraq at this point... we need a diplomatic surge."

Before the speech, civil rights legend Joseph Lowery told the crowd, "We've heard a voice crying in the political wilderness, and the sound we believe offers promise of policy and practices that can hasten the healing and wind down the war."

Lowery marched across the Pettus Bridge with Obama last month in Selma, Alabama. Lowery has not officially endorsed anyone in the campaign, but spoke glowingly of Obama's candidacy.

"My presence indicated the direction my heart is leaning," he told CNN. Lowery said the time may not right for an official endorsement, but "my presence there ought to be enough to satisfy those who look for formal endorsements."

Obama described the Selma event in his speech as "a solemn moment for me." But Obama said he believed the meaning of the day was lost on some people in the nation's capital.

"When I returned back to Washington, I met some of these folks who see politics only as a matter of lobbyists, checks and special interests," Obama said. "Some of them kind of patted me on the back, and they said that was very nice celebration of African-American history. And I looked at a couple of these folks, and I said, 'No, no. You don't understand. That was a celebration of American history.'"