The United States picked a public health expert of South Korean origin as its candidate for the World Bank presidency, a job emerging market economies are contesting for the first time.

In an announcement on Friday at the White House President Barack Obama said he was nominating Jim Yong Kim, president of Dartmouth College in New Hampshire and former director of the Department of HIV/AIDS at the World Health Organization.

It is time for a development professional to lead the world's largest development agency, Obama said flanked by Kim, Treasury Secretary Timothy Geithner and Secretary of State Hillary Clinton.

Angola, Nigeria and South Africa have endorsed the nomination of Nigerian Finance Minister Ngozi Okonjo-Iweala, a respected economist and diplomat, as a candidate to take over the bank when Robert Zoellick steps down in June.

The endorsement is in line with the belief that the appointment of the leadership of the World Bank and its sister institution, the International Monetary Fund, should be merit-based, open and transparent, the three said in a statement.

It was a rare example of unity among countries often at loggerheads as they strive for dominance on the continent.

Meanwhile, a spokeswoman for U.S. economist Jeffrey Sachs said he was withdrawing his nomination in support of Kim.

Professor Sachs supports Dr Kim 100 percent and with complete enthusiasm, spokeswoman Erin Trowbridge said.

The United States has held the presidency since the bank's inception after World War Two, and a European has always headed the IMF.

Brazil would like to nominate former Colombian finance minister Jose Antonio Ocampo, but said it cannot do so without Colombia's support, which now looks unlikely.

While Ocampo had agreed to stand and Brazil was willing to nominate him, Colombian Finance Minister Juan Carlos Echeverry said on Thursday his country was instead focusing on a bid for the presidency of the International Labour Organization.

He said that effort had a greater chance of success than going for the World Bank job because Colombia already held the top post at the Inter-American Development Bank.

Russia, a member of the so-called BRICs caucus of large emerging market economies, has refrained from publicly backing a non-U.S. candidate and instead called for a greater role for them in top management at international financial institutions.

Although the World Bank board would like to reach a consensus, Washington retains the largest single voting share and could expect the support of European nations and Japan, the bank's second-largest voting member.

The rise of emerging economies such as China, India and Brazil has put pressure on the United States and Europe to throw open the selection process for both the bank and the IMF.

Last year, all of the bank's 187 member countries agreed on a transparent, merit-based process to select a president.

FRIDAY DEADLINE

The deadline for nominations is 6 p.m. Washington time (10.00 p.m. British time) on Friday. The World Bank board of member countries will then shortlist three candidates and finalize its choice by the time of the IMF and World Bank semi-annual meetings on April 21.

The new head of the bank will take over at a time when the euro zone debt crisis is slowing the global economic recovery, undercutting demand in emerging and developing markets.

That person will have to decide how best to deploy resources in a budget-cutting environment in which large bank shareholders such as the United States are demanding results-based development, more transparency and greater efforts to tackle corruption.

Nancy Birdsall, president of the Center for Global Development in Washington, said earlier the nomination of a credible candidate such as Okonjo-Iweala upped the ante for the U.S. to have a really strong candidate.

It is a sign that we're living in a world where the geopolitical landscape is shifting and the U.S. can't do things by itself, she said.

(Editing by Timothy Ahmann, John Mair, Jeremy Gaunt and James Dalgleish)