The Central Intelligence Agency has closed a unit that for a decade had the mission of hunting Osama bin Laden and his top lieutenants, intelligence officials confirmed Monday. The unit, known as Alec Station, was disbanded late last year and its analysts reassigned within the C.I.A. Counterterrorist Center, the officials said. The decision is a milestone for the agency, which formed the unit before Osama bin Laden became a household name and bolstered its ranks after the Sept. 11 attacks, when President Bush pledged to bring Mr. bin Laden to justice dead or alive." "The efforts to find Osama bin Laden are as strong as ever," said Jennifer Millerwise Dyck, a C.I.A. spokeswoman. "This is an agile agency, and the decision was made to ensure greater reach and focus." Michael Scheuer, a former senior C.I.A. official who was the first head of the unit, said the move reflected a view within the agency that Mr. bin Laden was no longer the threat he once was. Mr. Scheuer said that view was mistaken. "This will clearly denigrate our operations against Al Qaeda," he said.