A file picture taken on December 20, 2011 shows Nigeria's Finance Minister Ngozi Okonjo Iweala. (PIUS UTOMI EKPEI/AFP/GETTY IMAGES)

Ngozi Okonjo-Iweala, Nigeria’s finance minister, is Africa’s standard-bearer in the contest to become World Bank president. Jose Antonio Ocampo, a former Colombian finance minister, is being championed by South America.

Both say they are better qualified for the job than the American candidate tapped by President Obama last week. But beyond that, each says the other would be better than Obama’s pick.

The White House nominated Dartmouth College President Jim Yong Kim for the top World Bank post, instantly making him the front-runner to replace Robert Zoellick when he leaves office in June. Under a gentleman’s agreement that goes back 60 years, the U.S. government gets to name the World Bank chief. But this time around, the American pick — and the U.S. prerogative — are being aggressively challenged.

In interviews, Okonjo-Iweala and Ocampo acknowledged that Kim has unquestioned expertise in public health. But they said public health is a narrow slice of what the World Bank does and an issue that many other global organizations address.

“He is known as a health expert who has helped developing countries and I have great respect for what he has been able to do. When you look at my experience you can see I have breadth and depth,” Okonjo-Iweala said in a telephone interview this week from Delhi, where she was working to gather support for her candidacy. “You cannot just look at health and view development through that lens, or just at agriculture or manufacturing — there are so many inter-relationships.”

Okonjo-Iweala, a former World Bank managing director, says she would make the institution faster to respond when countries need help if she were chosen as its next president. She would also increase its focus on creating jobs and addressing the massive need for roads, ports and other infrastructure in the developing world.

Ocampo, speaking by phone from his home in New York, where he teaches at Columbia University, said: “We are talking about the major development institution in the world. I can safely say that if they want to evaluate the candidates on their experience in development there is no question the finance minister of Nigeria and myself have a clear advantage.”

Ocampo, who has also been a senior U.N. official and prolific academic, says he would put emphasis on helping poor and middle-income countries manage the effects of climate change. He says he would also represent a bridge between the World Bank’s practical focus and the new ideas brewing in academia.

Kim, a physician and founder of the Partners in Health program, is on a world “listening tour” to further his own candidacy. U.S. Treasury officials are accompanying him and said he was not available for an interview. In a letter to World Bank directors, who will choose the new president, Treasury Secretary Timothy F. Geithner asked them to support the U.S. candidate. Geithner said Kim “brings the combination of experience, innovation and drive that will best serve the bank.”

Both Okonjo-Iweala and Ocampo said they want their nominations to prompt an earnest debate on the 25-member executive board about who is most qualified. The three candidates are to be interviewed separately on April 9, 10 and 11, with a decision expected before World Bank spring meetings that begin April 20.

Okonjo-Iweala and Ocampo also said they want their candidacies to provoke a debate about the nature of the World Bank itself. “This is not about symbolism. It is too important,” said Okonjo-Iweala, whose candidacy was endorsed by the African Union this week . “We are in it to get there. . . . We have been locked out of the system for the past 60 years.”

“That old system has to be finished,” said Ocampo. “I hope it is finished this time.” He was nominated by the bank’s executive director from Brazil, one of several rapidly developing countries that at a meeting in India this week called for reforms to give emerging economies more say at the World Bank and International Monetary Fund.

The power to make decisions at the World Bank and IMF is allocated according to a formula that takes into account each member country’s economic might and its financial contribution to the two institutions. Updating this formula is a sensitive process that can give a country more clout but also require that it increase its contributions. Most recently, proposed changes at the IMF would see Europe surrender two board seats to developing nations.

In the contest to head the World Bank, Kim starts with 15.74 percent of the votes in his pocket — the U.S. voting share on the bank board. By contrast, China, the world’s second-largest economy, has a 2.67 percent voting share. Africa as a whole has about 5 percent. South America has about the same — though some major Latin nations such as Mexico and Venezuela are represented by an executive director from Spain.

It would not take much for Kim to get close to the majority vote needed to win. Support from major U.S. allies, including Japan and the leading European nations, would be enough. Their backing is all but assumed, particularly since the United States deferred to Europe’s choice last year of the French finance minister, Christine Lagarde, to head the IMF and honors Japan’s traditional right to appoint the head of the Asian Development Bank.

But the two other candidates for World Bank chief insist they have a chance. Ocampo says that developing-world officials were quick out of the gate to rally support for their candidates. Last year, in the IMF contest, Lagarde had won a near majority through European endorsements before her challenger, Mexican central bank Governor Agustin Carstens, entered the race.

In the weeks after Zoellick announced he would be leaving the World Bank, finance ministers from top developing countries agreed they should put forward candidates, and support started building for Okonjo-Iweala and Ocampo.

The two candidacies are a sign of more cohesion among developing nations, Ocampo said. “It is essential that developed countries are willing to take this race as a competitive one.”

“I am hoping for the best,” said Okonjo-Iweala. “I am hoping that the shareholders of the World Bank will do what they promise. I am asking for a fair chance.”