WASHINGTON (AP) _ John Hamre, the deputy secretary of defense, is resigning to become head of a major Washington-based think tank, a senior defense official said today.

Rudy deLeon, the undersecretary of defense for personnel and readiness, will be nominated to replace Hamre in the No. 2 Pentagon post, the official said, speaking on condition of anonymity.

The Pentagon planned to announce today that Hamre would leave at the end of March and become head of the Center for Strategic and International Studies, the official said. Hamre has held the job since 1997. Before that he was the Pentagon's comptroller.

Cohen accepted Hamre's resignation last week, and Hamre informed his staff today.

Hamre took the lead role in preparing the Defense Department's far-flung computer networks for the Y2K rollover.