UNITED NATIONS — Rotating positions among long-serving officials, Secretary-General Ban is set to announce as early as today the appointment of a Swedish diplomat, Staffan de Mistura, as his personal envoy to Iraq, close aides said.

Yesterday, Mr. Ban announced that his current Iraq envoy, Ashraf Qazi of Pakistan, will be sent to Sudan. The envoy rotation will take place November 4, when Mr. Qazi will end his three-year stint in Iraq.

Although the decision was made weeks ago, Mr. de Mistura’s Iraq appointment had to wait until President al-Bashir of Sudan agreed to the appointment of Mr. Qazi, an aide to Mr. Ban said. The aide, who requested anonymity, added that Mr. Bashir finally gave the nod during a Monday dinner in Khartoum with Mr. Ban.

Several outside candidates of international stature dropped out of contention for the posts in Iraq and Sudan recently, leaving Mr. Ban to choose among U.N. veterans, another U.N. official said yesterday. In a recent Washington Post interview, the official noted, the American ambassador to the United Nations, Zalmay Khalilzad, signaled that sending Mr. de Mistura to Iraq may merely serve as a stopgap measure.

“A more prominent international figure could be invited to lead the Iraq talks in the future,” Mr. Khalilzad said.

In January 2005, after Mr. de Mistura served four years as U.N. envoy in Beirut, Mr. Ban’s predecessor, Kofi Annan, appointed him as Mr. Qazi’s deputy in Iraq. But the relationship between the two was said to be icy, and by the summer of 2006 Mr. de Mistura was replaced as Iraq deputy.

Mr. Annan made Mr. Qazi his top Iraq envoy in 2004, a year after the United Nations withdrew all its staffers in the aftermath of the car bombing of its Canal Hotel headquarters in Baghdad that killed special envoy Sergio Vieira de Mello and 21 others.

While Mr. Qazi failed to carve out a significant role for the United Nations in Iraq, he became entangled in a corruption investigation during the height of the oil-for-food scandal. Mr. Qazi was finally cleared of any wrongdoing in a July 3, 2006, report by the U.N. watchdog known as the Office of Internal Oversight Services.

Critics at the time faulted the investigation, however, saying that before the OIOS team started its work, Mr. Annan’s top aides said publicly that the investigators had assured them that Mr. Qazi would be exonerated. The investigation was conducted by an OIOS unit that at the same time cleared of wrongdoing a procurement officer, Sanjaya Bahel, who subsequently was convicted in a federal bribery case.