GENEVA — The head of the U.N. intellectual property agency gave an apparently false birth date that made him nine years older when he applied to join the body, an inaccuracy that may have helped him get hired and win promotions, a U.N. audit showed.

The confidential report, obtained by the Associated Press, said Kamil Idris changed his age back to the younger one last year — more than two decades after he had joined the World Intellectual Property Organization — a change that could enhance his retirement benefits. He has headed the agency since 1997.

The audit also raises questions about whether Mr. Idris gave incorrect information about his work history and college degrees before joining the United Nations.

Mr. Idris, a Sudanese citizen, says he gave the wrong age due to a typographical error when he first applied to work for the agency in 1982. He rejects allegations he sought to benefit from the misstatement, or from the correction.

An internal investigator has refrained from saying which birth year — 1945 or 1954 — he thinks is correct. But his 35-page report lays out how the differences could have affected on Mr. Idris’s career advancement and any future departure package.

Mr. Idris was hired in 1982 for a job requiring a decade of experience. He claimed to be 37, the same age as the other two candidates, said the audit. According to his revised account, he was 28.