Evan Vucci, Associated Press
Sen. Barack Obama is expected to receive the endorsement of his chief presidential campaign rival, Sen. Hillary Rodham Clinton, on Saturday.

Sen. Hillary Rodham Clinton will endorse Sen. Barack Obama on Saturday, bringing a close to her 17-month campaign for the White House, aides said. Her decision came after Democrats urged her Wednesday to leave the race and allow the party to coalesce around Obama.

Howard Wolfson, one of Clinton's chief strategists, and other aides said she would express support for Obama and party unity at an event in Washington, D.C., that day. One adviser said that Clinton would concede defeat, congratulate Obama and proclaim him the party's nominee, while pledging to do what was needed to assure his victory.

Her decision came after a day of conversations with supporters on Capitol Hill about her future now that Obama had clinched the nomination. Clinton had, in a speech after Tuesday night's primaries, suggested she wanted to wait before deciding about her future, but in conversations throughout the day Wednesday, her aides said, she was urged to step aside.

Clinton's decision came as some of her most prominent supporters — including former Vice President Walter F. Mondale — announced they were now backing Obama.

"I was for Hillary — I wasn't against Obama, who I think is very talented," Mondale said. "I'm glad we made a decision, and I hope we can unite our party and move forward."

One of Clinton's aides said they were told that except for her senior advisers, there was no reason to report to work after Friday, and that they were invited to Clinton's house for a farewell celebration that afternoon. The announcement from Clinton was moved to Saturday to accommodate more supporters who wanted to attend, aides said. "Sen. Clinton will be hosting an event in Washington, D.C., to thank her supporters and express support for Sen. Obama and party unity," said Wolfson.

Obama, not even waiting for a formal concession from Clinton, announced a three-member vice presidential selection committee that will include Caroline Kennedy, who has become a close personal adviser since endorsing him four months ago.

Robert L. Johnson, the founder of Black Entertainment Television and a leading contributor to Clinton, urged members of the Congressional Black Caucus to lobby Obama to pick Clinton as his running mate. He said he had spoken to Clinton about it and was speaking with her permission.

"We need to have the certainty of winning," Johnson wrote in the letter on Wednesday. "And, I believe, without question, that Barack Obama as president and Hillary Clinton as vice president bring that certainty to the ticket."

David Plouffe, campaign manager for Obama, said the senator feels no pressure to swiftly name a vice presidential candidate to either tamp down the speculation about Clinton's future role or allay her dejected supporters. The passage of time, he said, would heal the fissures and hard feelings that developed during the primary fight as Democrats turned their complete focus to Sen. John McCain of Arizona, Obama's likely opponent.

Pivoting toward the general election battle, McCain and Obama both said they were interested in holding a series of Lincoln-Douglas-style town hall debates across the country this summer.

Obama's decision to announce his vice presidential search committee on Wednesday was intended to mute the speculation about Clinton's interest in the position. At the same time, Mondale — who in his career has served as a vice president, and picked one — suggested that Clinton and her supporters pull back from even the appearance of campaigning for the No. 2 spot, suggesting it could complicate a critical decision by Obama while undercutting Clinton's prospects.

"I think it's best he just be left alone," he said. "It really ought to be an unpressured."

Obama and Clinton crossed paths briefly in Washington on Wednesday, but aides said they did not linger long enough to discuss the unfinished business hanging over them. As he left the Capitol, Obama told reporters, "We're going to have a conversation in the coming weeks."

Obama appeared before the American Israel Public Affairs Committee, where, tacking to the right, he described a far tougher series of sanctions he would be willing to impose on Iran than he had outlined during the campaign. Clinton, during an earlier appearance there, moved to reassure an audience clearly nervous about Obama's views on Israeli security.

"I know that Sen. Obama will be a good friend to Israel," she said.

Aides to Obama and Clinton said that in the days ahead, at least some of Clinton's fundraisers would move to join the ranks of the Obama campaign. Still, with the realization of defeat still settling in, it appeared that most of her major financial backers were holding back until they got a clearer signal from Clinton of her intentions.

"I'm being aggressively courted by folks in the Obama campaign," said Mark Aronchick, a Philadelphia lawyer who is Clinton's Pennsylvania finance chairman. "I've told them all, 'Everybody relax. Take a deep breath. There's time enough here.'"

Today, Obama planned to head to the southwestern tip of Virginia, the heart of Appalachia, to begin courting voters in a state that traditionally goes Republican, but could be a fall battleground. Then, Obama intends to take a few days away from his public schedule to strategize privately about the general election campaign.

Clinton's decision to suspend her campaign, which was first reported by ABC News, was a bow to the emerging political reality. No one in her campaign — including by all reports Clinton herself — saw a viable road to the nomination. A suspension of the campaign allows her to continue raising money and pay off her millions of dollars in debt.

The desire of the party for Clinton to leave the race was signaled — if politely — as four top Democratic leaders issued an early morning statement asking all uncommitted delegates to make their decisions by Friday. The statement from the Democratic chairman, Howard Dean, House Speaker Nancy Pelosi, Sen. Harry Reid and West Virginia Gov. Joe Manchin, stopped short of endorsing Obama, but aides said they would likely move in that direction if Clinton lingered in the race.

"The voters have spoken," they said in a joint statement released before 7 a.m., purposefully timed to set the tone for the day after the election. "Democrats must now turn our full attention to the general election."

Rep. Rahm Emanuel, D-Ill., who has close ties to Obama and Clinton, and who had kept studiously neutral throughout the fight, said in an interview that he was "coming out from my desk" to endorse Obama. "The fact is that he is the nominee," Emanuel said

He seemed quizzical at the slowness of Clinton's decision not to acknowledge this. "You don't answer about whether you want to be about vice president unless there's no doubt in your mind that he is the nominee," he said, referring to Clinton's initial reluctance to congratulate Obama, noting that she told supporters she would be open to be vice president, if Obama wanted her.

Clinton's initial ambivalence about her future in her speech on Tuesday night stirred concern among some of her top supporters.

"By the time she got on that podium last night, she knew it was over and that she had lost," Hillary Rosen, one of Clinton's most prominent women supporters, wrote on Huffington Post. "I am sure I was not alone in privately urging the campaign over the last two weeks to use the moment to take her due, pass the torch and cement her grace."

"I am also so very disappointed at how she has handled this last week," Rosen wrote on HuffingtonPost.com.


Contributing: Carl Hulse and Michael Luo