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 that day. One adviser said Clinton would concede defeat, congratulate Obama and proclaim him the party’s nominee, while pledging to do what was needed to assure his victory in November.

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 on Wednesday, her aides said, she was urged to step aside.

“We pledged to support her to the end,” Representative Charles B. Rangel, a New York Democrat who has been a patron of Clinton since she first ran for the Senate, said in an interview. “Our problem is not being able to determine when the hell the end is.”

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. The announcement from Clinton was moved to Saturday to accommodate more supporters who wanted to attend, aides said.

“Senator Clinton will be hosting an event in Washington, D.C., to thank her supporters and express her support for Senator Obama and party unity,” Wolfson said.

Obama, not 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.

With some Democrats promoting Clinton as Obama’s No. 2, his aides said they would move slowly in the search, allowing passions from the bruising primary battles to cool.

“Now that the interfamily squabble is done,” Obama said Wednesday evening at a Manhattan fund-raiser, “all of us can focus on what needs to be done in November.” Earlier Wednesday, Obama and Clinton crossed paths briefly in Washington. 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 heretofore.

Clinton, in a later appearance before the group, moved to reassure an audience clearly nervous about Obama’s views on Israeli security. “I know that Senator Obama will be a good friend to Israel,” she said.

Turning to the general election, Senator John McCain of Arizona, Obama’s likely opponent, and Obama both said they were interested in holding a series of debates this summer.