WASHINGTON — Jim Yong Kim, who on Sunday took over as World Bank president, said his first task will be to help developing nations keep growing at a time of stress for the world economy.

“We begin our work together at a crucial moment” as the world economy “remains vulnerable,” Kim wrote in an e-mail to the Washington-based bank’s staff obtained by Bloomberg News. “My immediate priority will be to intensify the Bank Group’s efforts to help developing countries protect growth and jobs.”

The 52-year-old Kim, the former president of Dartmouth College, succeeds Robert Zoellick at the helm of a poverty-fighting institution that made loans worth almost $53 billion last year. Kim, a physician by training, has little time to ease into a job that stretches beyond his expertise as global growth is threatened by the European debt crisis and a slowdown in China.

Besides the immediate challenge, Kim said in the memo, the bank stands ready to support countries in their longer-term growth strategies.