The U.N. bureaucracy's most senior American and a key official in the world body's management reform efforts announced his resignation on Thursday as a new secretary-general prepares to take over. Christopher Burnham, the U.N. undersecretary-general for management, will leave November 15 for a job in the banking sector, six weeks before South Korean Foreign Minister Ban Ki-moon is to succeed Kofi Annan as the new U.N. leader. “Chris has been a driving force in the management reform efforts over the past 18 months,” Annan said, citing his help in creating a new ethics office, stronger financial rules and accounting standards, and procurement reforms.