In a 37-minute speech at the National Constitution Center, perhaps the most momentous of his 13-month campaign for president, Obama sought to stem the political damage to his campaign caused by his former pastor's racially inflammatory remarks.

For the first time, Obama publicly acknowledged he had heard some "controversial" remarks from the Rev. Jeremiah Wright, his spiritual mentor and former pastor of the Trinity United Church of Christ in Chicago. He condemned remarks in some of Wright's sermons that blamed the U.S. for the Sept. 11 terrorist attacks and accused America of being irredeemably racist.

"I can no more disown him than I can disown the black community," Obama said, speaking in front of eight American flags. "I can no more disown him than I can my white grandmother - a woman who helped raise me, a woman who sacrificed again and again for me, a woman who loves me as much as she loves anything in this world, but a woman who once confessed her fear of black men who passed her by on the street, and who on more than one occasion has uttered racial or ethnic stereotypes that made me cringe."

The speech comes after racial conflicts arose in the campaign in recent days, both as a result of Wright's comments and remarks by former vice-presidential candidate Geraldine Ferraro, a supporter of Hillary Rodham Clinton, who said that Obama would not be in his position as the frontrunner for the Democratic nomination if he were a white man or woman.

Wright, Obama said, brought him to his Christian faith, married him, baptized his daughters and taught him the moral imperative of Christianity and other religions to love one another, and to lift up the poor and downtrodden.

Wright has said the U.S. government unleashed AIDS and the crack cocaine to oppress black people, and also called America the "U.S. of KKKA" and has said the nation is the "number one killer in the world." In 2003, Wright said in a sermon, "The government gives them the drugs, builds bigger prisons, passes a three-strike law and then wants us to sing 'God Bless America.' No, no, no, God damn America, that's in the Bible for killing innocent people."

The controversy threatened to swallow Obama's candidacy, premised as it is in large measure on the idea that can transcend traditional racial divisions and unite the country. Obama in the past has made racial issues and his personal story relatively minor parts of his message, but he said Monday he recognized he likely would not become the Democratic nominee without a forthright framing of his views on the role of race in politics.

Obama said: "Reverend Wright's comments were not only wrong but divisive, divisive at a time when we need unity; racially charged at a time when we need to come together to solve a set of monumental problems – two wars, a terrorist threat, a falling economy, a chronic health care crisis and potentially devastating climate change; problems that are neither black or white or Latino or Asian, but rather problems that confront us all."

He said that the remarks and the anger they reflect do not take into account the progress the nation has made in race relations and called America's ability to change the "genius" of its people and its government.

Obama was interrupted perhaps a dozen times by applause, but for great chunks of the speech the audience was absolutely still and the only thing that could be heard was the clicking of the motors of still cameras.

Obama was introduced by former Sen. Harris Wofford (D., Pa.), a veteran of the civil rights movement and former aide to President John F. Kennedy.

Wofford said that Obama has the quality that has "distinguished our finest presidents. . .the quality of being an original, whose gifts and capacity for leadership match the needs of the moment."

Contact staff writer Thomas Fitzgerald at 215-854-2718 or tfitzgerald@phillynews.com.