“This is not a call for the United Nations to do less, though that might be one result,” he told the General Assembly. “It is a call for it to do better.”

He said the review “could have a lasting impact not only on what we do, but on how we do it.”

The decision to conduct the review, which was taken by national leaders attending the 2005 World Summit at the UN, “was one of the most meaningful and potentially historic” of the session, Mr. Annan said, while cautioning that the process poses a “daunting challenge.”

In order to facilitate the work of Member States the UN has set up a searchable electronic registry of still-active mandates originating from the resolutions of the General Assembly, the Security Council and the Economic and Social Council.

“The review of mandates is a unique opportunity to strengthen and adapt our Organization to the priorities of today,” the Secretary-General told delegates. “I am sure you will not fail to seize it.”