Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said on Sunday that air strikes in Libya had been "so far very effective" but that "it's difficult to know" what would happen to Libyan leader Muammar Qaddafi in the coming weeks.
In an appearance on CBS' "Face the Nation," the U.S.'s top military officer said he expects the U.S. will hand over leadership on the military operation in Libya to a broader international coalition in the coming days, but emphasized that Qaddafi's future - and the depth of his resistance - remained indeterminate.
"He's a thug, he's a cagey guy, he's a survivor," Mullen told CBS' Bob Schieffer. "We know that. So it's difficult to know exactly how it comes out, but in the immediate future we're very focused on protecting, providing the environment in which the Libyan civilians cannot be massacred by him and that there can be humanitarian relief and particularly in and around Benghazi."
White House national security spokesman Tommy Vietor told Politico that the U.S. mission was to protect Libyan civilians from violence -- not to guarantee a change in leadership.
"We still believe that Qaddafi has lost his legitimacy to lead and must go," he said. "However, the goal of this resolution is not regime change. Rather, it authorizes the use of force with an explicit commitment to pursue all necessary measures to stop the killing. These two things aren't contradictory."
U.S. and international allies fired missiles and bombs at Libya in an overnight strike last night - but Qaddafi has refused to yield, firing back with defiance and threats.
"His reaction has been the usual kind of bluster and defiance," Mullen said.
Mullen said he considered the operation "very, very effective" so far, and emphasized what he considered its narrow focus.
The mission, he said, is "clearly defined" to establishing a no-fly zone over Libya and protecting the Libyan people from Qaddafi - whom he described as "a guy who has killed his own civilians ruthlessly in the past."
"We're focused on supporting the Libyan people from a humanitarian standpoint," Mullen said. "I think it's important to point out that the Libyan people asked for help here. This wasn't something that the United States ginned up. This was something that an awful lot of countries including the people most affected have asked for help."
Sen. Richard Lugar, the top Republican on the Foreign Relations Committee, argued however that the operation lacked sufficient clarity - and that Congress should be consulted "if we're going to war with Libya."
"We are not declaring war at this point," he told Bob Schieffer on "Face the Nation." "We are a part, as the admiral has said, of a coalition. We've already fired 110 missiles, tomahawks at Libya, and had some aircraft support. But my point this week publicly has been that if we're going to war with Libya we ought to have a declaration of war by the Congress."
"Before we go to war there always ought to be a plan for what is going to proceed," he continued. "That's especially important in this case because the mission right now is based, as the admiral said, on trying to relieve the civilians in Libya from a tyrant. From trying to make sure that the cruelties and the murder and what have you doesn't continue. But how do you do that?"
"We really have not discovered who it is in Libya that we are trying to support," he continued. "Obviously the people that are against Qaddafi - but who?"
"We had better get this straight from the beginning," Lugar said. "Or there is going to be a situation in which war lingers on - country after country, situation after situation - all of them on a humane basis, saving people."Complete coverage: Anger in the Arab World
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He confirmed that Qaddafi had a large store of mustard gas in Libya, but said he did not see indications that Qaddafi planned to use it.
"He does have stores of that - a significant quantity - we've had our eyes on that for a significant period of time," Mullen said. "There's no indication that he is moving toward that, but certainly that's something we're watching very carefully."
"Certainly, he could do a lot of damage with and it would require action to prevent that should he move in that direction - but I honestly haven't seen him move in that direction," he continued.