June 4 (Bloomberg) -- Barack Obama, in his first day as the presumptive Democratic presidential nominee, named Caroline Kennedy Schlossberg, Jim Johnson and Eric Holder to lead the search for a running mate.

All three have strong ties to Washington. Kennedy Schlossberg is the daughter of former President John F. Kennedy. Johnson served as chief executive officer of the government- chartered mortgage-finance company Fannie Mae, and Holder worked as a deputy U.S. attorney general under President Bill Clinton.

Obama, 46, an Illinois senator, will depend on the three for advice as pressure mounts to ask his vanquished rival, New York Senator Hillary Clinton, to join the ticket. Johnson helped select running mates for past Democratic nominees John Kerry and Walter Mondale.

``Senator Obama is pleased to have three talented and dedicated individuals managing this rigorous process,'' Obama spokesman Bill Burton said. ``He will work closely with them in the coming weeks, but ultimately this will be his decision and his alone.''

Many of Clinton's supporters are pushing Obama to pick her, saying it would help unify the party. Clinton has gained leverage by winning nine of the last 16 contests in the nominating process and claiming strong support among women and working-class voters.

No Concession Yet

Clinton, 60, hasn't yet conceded, though she has put out word she is open to a vice presidential nomination. Robert L. Johnson, founder of Black Entertainment Television and a longtime Clinton backer, yesterday sent a letter to House Majority Whip James Clyburn asking him to urge the Congressional Black Caucus to support Clinton as a running mate.

``As African Americans we agree that the stakes in this election are far too high to take any chances that this party will not be unified from the top to the bottom in our effort to gain control of the White House,'' Johnson wrote. Both candidates ``have demonstrated that they have the courage and the ability to inspire and lead this nation to greatness today and for years in the future,'' he said.

Democratic strategists and activists have suggested a host of names. Among them are former vice presidential nominee John Edwards and Senators Christopher Dodd of Connecticut, Joseph Biden of Delaware and James Webb of Virginia.

Rallying to Obama

Other party leaders and lawmakers began coalescing around Obama and urging Clinton to close out her campaign.

The day brought another string of superdelegate endorsements for Obama, including New Jersey Senator Frank Lautenberg, who had been one of eight uncommitted Democrats in the Senate. On the House side, Democratic Caucus Chairman Rahm Emanuel, former domestic policy adviser to Bill Clinton, also endorsed Obama. Like Obama, Emanuel represents Illinois.

Senate Majority Leader Harry Reid, House Speaker Nancy Pelosi, Democratic Governors' Association Chairman Joe Manchin, and Democratic National Committee Chairman Howard Dean pressed the remaining superdelegates to make up their minds.

``Democrats must now turn our full attention to the general election,'' they said in a joint statement. ``We are urging all remaining uncommitted superdelegates to make their decisions known by Friday of this week so that our party can stand united.''

Some Clinton supporters expressed frustration that she hasn't bowed out. In an interview with ABC News, Representative Charles Rangel, one of Clinton's staunchest supporters, said it is time for Clinton to publicly state her future plans and allow her supporters to switch their allegiance to Obama.

``Unless she has some good reasons -- which I can't think of -- I really think we ought to get on with endorsements'' of Obama, the New York Democrat said.

To contact the reporters on this story: Kristin Jensen in Washington at kjensen@bloomberg.net; Chris Dolmetsch in New York at cdolmetsch@bloomberg.net.

Last Updated: June 4, 2008 18:30 EDT