Defense Secretary Donald H. Rumsfeld's top international policy adviser is leaving his post, in the first announced Pentagon departure since the secretary's resignation last week.

Peter W. Rodman, the assistant secretary of defense for international security affairs, will join the Brookings Institution as a senior fellow. Rodman's move has been in the works for months and was not triggered by Rumsfeld's resignation, according to Pentagon press secretary Eric Ruff.

Rodman, who began his career in government as an assistant to Henry Kissinger, has worked in five presidential administrations, including stints at the National Security Council and the State Department.

He has served as Rumsfeld's senior adviser on security strategy and policy involving the Middle East, Asia and Europe. He traveled recently with Rumsfeld on diplomatic visits to China and southeast Asia.

Rodman will be working with the Foreign Policy Studies Program at Brookings in the new year.

No date has been set yet for Rumsfeld's departure. President Bush has chosen former CIA director Robert Gates to replace Rumsfeld, and the Senate is expected to conduct a confirmation hearing as soon as next month.