|PIC1|US Democratic presidential candidate Barack Obama on Tuesday criticised his preacher's racially charged sermons but said he could not disown him in a speech urging Americans to move past their "racial stalemate".

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.

"These are difficult issues and we have seen that in this campaign. Race and gender are difficult issues. And therefore we need to have more discussion about them," she said.

Clinton picked up an endorsement from Pennsylvania Republican John Murtha, a leading congressional opponent of the war in Iraq. Murtha said Clinton was best placed to deal with the issues surrounding the war and the economy.

As the Democrats' battled it out, Arizona Senator McCain was holding his own in a CNN/Opinion Research Corp poll reflecting hypothetical matchups. Obama led McCain by two percentage points and Clinton led him by one.

McCain, who was on a Middle East and Europe swing, said in Jordan that a US troop build-up in Iraq is succeeding and that a premature withdrawal would dramatically enhance Iran's influence in the region.

The Obama campaign is worried the uproar over the pastor's comments could cost him support with white voters in states like Pennsylvania, which holds an important voting contest on April 22.

A Quinnipiac University poll gave Clinton a lead over Obama of 53 to 41 percent in Pennsylvania, compared to a 49 percent to 43 percent lead over him in late February in that state.

"Did I know him to be an occasionally fierce critic of American domestic and foreign policy? Of course. Did I ever hear him make remarks that could be considered controversial while I sat in church? Yes. Did I strongly disagree with many of his political views? Absolutely," Obama said of Wright.

The Wright comments have threatened to overshadow Obama's central message that he would bridge divisions in the United States, including those involving race.

Last week, Geraldine Ferraro, a Clinton supporter and 1984 vice presidential candidate, attributed Obama's lead in the Democratic race to his being black.

Obama said the race discussion took a divisive turn when it was implied "my candidacy is somehow an exercise in affirmative action; that it's based solely on the desire of wide-eyed liberals to purchase racial reconciliation on the cheap."

Blacks took offense when Clinton's husband, former President Bill Clinton, in January compared Obama's victory in the South Carolina primary to success there by Jesse Jackson, a black candidate who ran for president in 1984 and 1988. Critics saw the remarks as a bid to marginalize Obama as a candidate only for black America.

But Bill Clinton told television interviewers on Monday it was a "myth" that his wife's campaign had engaged in racial politics in the Southern state where he said he "never said a bad word about Senator Obama - not one."

In his speech, Obama clearly disagreed.

"We saw racial tensions bubble to the surface during the week before the South Carolina primary," he said.