"I don't think there's any question that America is safer as a result of the bin Laden operation," Panetta told reporters aboard a military aircraft Friday.
"When you combine that with the other operations that have ... gone after al-Qaida leadership, I think it has weakened al-Qaida as an organization and certainly it has prevented them from having the command-and-control capability to be able to put together an attack similar to 9/11."
But he said al-Qaida is still a threat and the United States and its allies continue pursuing al-Qaida and other terrorists.
"The more successful we are at taking down those who represent their spiritual and ideological leadership, the greater our ability to weaken their threat to this country and to other countries," Panetta said.
Panetta, who was CIA director at the time of the raid that killed bin Laden, made the comments while returning from a week-long trip to South America to strengthen military ties in Colombia, Brazil and Chile, the Defense Department said.
Law enforcement agencies said this week there's no specific credible threat of a U.S. terror attack on the one-year anniversary of bin Laden's May 2 death.
Bin Laden was killed in a U.S. raid in Pakistan May 2 and his death brought calls for attacks on the United States.