WASHINGTON (CNN) -- Saying he is "deeply troubled" with the timing of National Intelligence Director John Negroponte's resignation, incoming House Intelligence Committee Chairman Jay Rockefeller, D-West Virginia, vowed to swiftly begin confirmation hearings for Negroponte's successor.

Negroponte is set to exit the top intelligence post without a second-in-command. Former Deputy Director of National Intelligence Gen. Michael Hayden left that position last May to become head of the Central Intelligence Agency, and his successor has yet to be confirmed.

"It is not acceptable for the top two jobs to be vacant at the same time, Rockefeller said in a statement. "The leadership of the Intelligence Community is too important."

A senior administration official tells CNN that President Bush plans to nominate retired Admiral Mike McConnell to succeed Negroponte.