WASHINGTON — Defense Secretary Robert M. Gates said Wednesday that he surmised that “somebody” in Pakistan had been aware that Osama bin Laden was hiding in a compound in the Pakistani garrison town of Abbottabad, but that there was no evidence so far that anyone in the country’s senior leadership had known.

“My supposition is, somebody knew,” Mr. Gates said at a Pentagon news conference with Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff. Beyond that, he said, the Obama administration, which has repeatedly said that Bin Laden seemed to have a “support network” while in hiding, had little information.

“We don’t know whether it was retired people, whether it was low level — pure supposition on our part,” Mr. Gates said. “It’s hard to go to them with an accusation when we have no proof that anybody knew.”

Mr. Gates said that his supposition, shared by many other Obama administration officials, did not extend to Pakistan’s top political and military officials. “I have seen no evidence at all that the senior leadership knew,” Mr. Gates said. “In fact, I’ve seen some evidence to the contrary.”