He also noted that a U.S. strike would be more effective than an Israeli one.
"If they decided to do it, there's no question that it would have an impact, but I think it's also clear that if the United States did it we would have a hell of a bigger impact," Panetta told the National Journal.
Shortly after the interview was published, White House Press Secretary Jay Carney also responded to a report in an Israeli newspaper that claimed the U.S. offered Israel high-tech weaponry like bunker-busting bombs and refueling planes in exchange for a pledge to hold off on attacking Iran until 2013.
Carney said "there was no such agreement proposed or reached" in meetings Obama held, without appearing to comment on what other officials might have discussed.
"We have ... high-level cooperation between the Israeli military and the U.S. military, at other levels with other agencies in their government and our government, but that was not a subject of discussion in the president's meetings," Carney said.
Defense officials, though, told Fox News that no "sweeteners" were offered to the Israelis during Netanyahu's visit. One senior Pentagon official said "no promises were made, no deals were struck, but weapons were discussed -- as you would expect in a meeting with the defense secretary."
Panetta, in the interview with the Journal, said the U.S. has been examining military options regarding Iran "for a long time."