The Office of Hawaiian Affairs is expected to pick a successor to longtime Administrator Clyde Namuo in the next three to five months, OHA Chairwoman Colette Machado said.

Namuo, 60, said he is stepping down Dec. 31 after 10 years as administrator and chief executive officer.

In the interim, OHA chief operating officer Richard Pezzulo will serve as acting administrator, Machado said. The search for a new administrator will be headed by OHA’s Asset Resource Management Committee, which is headed by trustee Oz Stender. Machado said the search would be aided by a professional recruitment company.

Namuo, whose contract with OHA ends July 31, 2012, said he and a majority of the board trustees agreed that he would leave at the end of the year to allow for an orderly transition.

Namuo, who said he is leaving the job of his own accord but added he has no immediate plans.