WASHINGTON (AFP) - Fallen White House contender Hillary Clinton Thursday promised to throw the full weight of her formidable support behind Democrat Barack Obama as she prepared formally to quit the race. Following concerted pressure from some of her own backers, frustrated at her refusal to bow out, Hillary announced she would end her dogged quest to be America's first female president on Saturday at an event in Washington. Hillary backers in the meantime renewed their pressure on Obama, on his own historic mission to become the first African-American president, to select their champion as his vice presidential nominee. "I will be speaking on Saturday (tomorrow) about how together we can rally the party behind Senator Obama," the former first lady said in an elegiac message to supporters. "The stakes are too high and the task before us too important to do otherwise," she said. "I have said throughout the campaign that I would strongly support Senator Obama if he were the Democratic Party's nominee, and I intend to deliver on that promise."Hillary had refused to concede late Tuesday, despite Obama's crossing the winning line of 2,118 delegates needed to become the Democratic standard-bearer in the presidential election against Republican John McCain. In November, voters must pick between Obama, 46, a freshman senator and charismatic champion of a new political generation, and McCain, 71, a Vietnam War hero who insists Obama would be a dangerous bet to lead the United States. The two have lost no time in crossing swords over Middle East diplomacy, on the Iraq war and on Obama's stated aim to launch direct talks with leaders in Iran and other "rogue states." The White House candidates were spending Thursday in states that could prove critical to victory in November - Obama in Virginia and McCain in Florida. Obama's takeover of national Democratic operations has picked up pace. The party said it was falling into line with his policy of refusing to accept donations from Washington lobbyists. "The American people's priorities will set the agenda in an Obama administration, not the special interests," Democratic National Committee Chairman Howard Dean said. At a fundraising dinner in New York, costing 28,500 dollars a plate, Obama late Wednesday paid tribute to Hillary's "extraordinary campaign." "Now that the inter-family squabble is done, all of us can focus on what needs to be done in November," he said, as the dust settled on five months of brutal primary campaigning. Hillary said: "My differences with Senator Obama are small compared to the differences we have with Senator McCain and the Republicans." But as sombre and tearful staff at Hillary's campaign headquarters outside Washington dismantled their operations, there was some anger at the belated nature of the New York senator's concession. The New York delegation to Congress, led by Representative Charles Rangel, said it was now throwing its support to Obama after appealing to Hillary, in a conference call Wednesday, to end the suspense. Rangel kept up a lobbying campaign for Obama to choose Hillary as his running mate, after she had told state colleagues on Tuesday that she was open to the idea. Noting Hillary's 18 million primary votes and victories in swing states, Rangel told CBS that "we should expect a landslide if they had this dream ticket." But Obama said he would not be rushed as a three-member team, including assassinated president John F Kennedy's daughter Caroline, began to vet vice-presidential contenders on his behalf. Interviewed by CBS, the Illinois senator reiterated: "Senator (Hillary) Clinton would be on anybody's short list, obviously."