Hillary Clinton will end her presidential bid and declare her support for Barack Obama, she said in a letter on Thursday, concluding a gruelling 16-month nominating fight that split the Democratic Party.

Clinton told supporters in the letter she would publicly back Obama on Saturday and also pledge to work for party unity in the general-election race against Republican John McCain.

"On Saturday, I will extend my congratulations to Senator Obama and my support for his candidacy," the New York senator and former first lady wrote.

"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."

Obama clinched the nomination on Tuesday, and Clinton spent the day on Wednesday talking to supporters - many of whom urged her to halt her campaign and begin bringing the party together.

Clinton will thank her supporters at the event, which was originally planned for Friday but switched to Saturday to allow more supporters to attend.

"This has been a long and hard-fought campaign, but as I have always said, my differences with Senator Obama are small compared to the differences we have with Senator McCain and the Republicans," Clinton said in the letter.

"I will be speaking on Saturday about how together we can rally the party behind Senator Obama. The stakes are too high and the task before us too important to do otherwise."

Obama attended two fundraising events in New York City on Wednesday night and acknowledged her decision.

"Your junior senator from New York engaged in an extraordinary campaign," he told attendees at one fundraiser. "Now that the interfamily squabble is done, all of us can focus on what needs to be done in November."

CHOOSING A RUNNING MATE, DEBATING MCCAIN

McCain proposed that Obama join him for a series of joint summer town-hall meetings across the country. Obama's campaign manager called the idea appealing but made no immediate commitment.

In an interview with NBC News, Obama said he would not be rushed into making a decision about his running mate. He also said he would welcome former President Bill Clinton's help in the campaign.

"My strong feeling is that moving forward, I'm going to need Bill Clinton involved in this process," Obama said. "He still is a transcendent political figure in this country. And I want him involved."

Obama campaigns on Thursday in Virginia, a potential battleground state in November, with two prospective running mates from the state - Gov. Tim Kaine, an early supporter of Obama, and U.S. Sen. James Webb, a Vietnam veteran and former secretary of the Navy.

Obama, the first black candidate to lead a major U.S. party into a White House race, announced a three-member team to head his search for a vice president.

Caroline Kennedy, daughter of the late President John Kennedy, will vet prospective Obama running mates along with former Deputy Attorney General Eric Holder and Jim Johnson, former chief executive of the mortgage lender Fannie Mae, who performed the same task for Democrats John Kerry in 2004 and Walter Mondale in 1984.