Obama sought to quell a political firestorm ignited when news outlets called attention to sermons by the Rev Jeremiah Wright at Trinity United Church of Christ in Chicago, which the Illinois senator attended for two decades.
"We have a choice in this country. We can accept a politics that breeds division, and conflict, and cynicism," he said. "Or, at this moment, in this election, we can come together and say, 'Not this time.'"
Wright, who retired recently, has railed that the September 11 attacks were retribution for US foreign policy, called the government the source of the Aids virus and expressed anger over what he called racist America.
"I can no more disown him than I can disown the black community," Obama, who would be the first African-American president, said in a major speech about race in America.
The speech was entitled "A More Perfect Union", a line from the preamble to the U.S. Constitution that Abraham Lincoln cited in 1861 in arguing against the country splitting apart into North and South.
Flare-ups over race have roiled the campaign trail as Obama battles for the Democratic nomination with New York Senator Hillary Clinton, who would be the first woman president. They are vying for the right to face Republican candidate John McCain in the November election.
Obama said Wright's remarks were not simply controversial but instead "expressed a profoundly distorted view of this country - a view that sees white racism as endemic."
Obama said his own life as the son of a black man from Kenya and a white woman from Kansas had seared into his makeup the idea that racial divisions can be overcome.
"It's a racial stalemate we've been stuck in for years," he said. "But I have asserted a firm conviction - a conviction rooted in my faith in God and my faith in the American people - that working together we can move beyond some of our old racial wounds."
RACE AND GENDER
Clinton told reporters in Philadelphia she did not see or read Obama's speech but was glad he gave it.
