LONDON – With U.S., British and French forces now fully engaged in attacking Moammar Gadhafi’s military in Libya from the air and sea, and the chairman of the U.S. Joint Chiefs of Staff declaring that a no-fly zone is in effect, the question becomes: How does this end?

The United Nations Security Council resolution that authorized the attacks defines the goal as a cease-fire that stops Gadhafi from assaulting his people.

President Obama on Thursday added to that by saying that Gadhafi “must stop his troops from advancing on Benghazi, pull them back from Ajdabiya, Misrata, and Zawiya” — three cities that had at one time been under rebel control — “and establish water, electricity and gas supplies to all areas.”

And, Obama said, “Humanitarian assistance must be allowed to reach the people of Libya.”

But whether such a cease-fire could leave Gadhafi in power remains an open question. Neither the U.N. nor Obama have said explicitly that Gadhafi must be removed from power, although Obama had previously called on Gadhafi to step down.

On Sunday, Michele Flournoy, U.S. defense undersecretary for policy, implied in an interview with the BBC that nothing short of a Gadhafi departure from power was acceptable. “He’s lost his legitimacy,” she said.

Still, Flournoy was unwilling to say explicitly that Gadhafi had to go in order for the U.S.-led campaign to end. “It’s too early to speculate as to where this ends up,” she said.

Adm. Mike Mullen, the chairman of the U.S. Joint Chiefs of Staff, was similarly reluctant to make any long-term predictions in an interview with ABC News.

Describing the military objective as “limited,” he dodged a question about whether the no-fly zone over Libya might remain in place for as long as the United States enforced a similar zone over Iraq — 12 years. “Circumstances will drive where this goes,” he said.

That troubles some military analysts, who worry that the West’s urgent action over the weekend isn’t backed by planning for what sort of Libya will be left behind when the aerial campaign stops.

It also troubles leading lawmakers on Capitol Hill.

“Before any further military commitments are made, the administration must do a better job of communicating to the American people and to Congress about our mission in Libya and how it will be achieved.” House Speaker John Boehner, R-Ohio, said Sunday.

“I think we’re seeing the opening shot of a fairly long campaign,” said retired Royal Navy Rear Adm. Chris Parry, a former top planner for Britain’s Defense Ministry. Calling the airstrikes against Libya a “something-must-be-done strategy,” Parry said he’d seen no “evidence of a long-term strategy.”

The U.N. resolution “only takes us so far,” he said. “Some thought has got to be given to what comes next.”

Paul Pillar, a professor at Georgetown University in Washington who spent nearly three decades as a senior U.S. intelligence analyst, said that on its face, the U.N. resolution offers no formula for ending the West’s military obligations. “If the mission is to protect Libyans, this is a mission that inherently has no end,” he said, as long as Gadhafi remains in power.

That could certainly happen, Pillar said. “A central fact is the disunity of Libya, which is stitched together from three parts,” he said. “It is plausible that (Gadhafi) would hold out in the west even if the eastern part of the country remains” in rebel hands.

The specter of an Iraq-like commitment that lasts years and leaves the West ultimately setting up a post-Gadhafi government hovers over the entire operation. Former British Army commander Michael Jackson unintentionally made that point during an interview with the BBC Sunday morning.

“The political goal has got to be a stable Iraq,” Jackson said in response to a question about how the conflict might end. The interviewer immediately interrupted — “You mean Libya,” she said.

“What did I say?” Jackson asked. Told he had said Iraq, the retired general — who led the British army when the Iraq war began — chuckled. “Forgive me, a Freudian slip.”

Jackson said he had no inside knowledge of what is under consideration for Libya.

Jackson went on to outline a scenario that included a diplomatic arrangement in which Gadhafi remains in power.

But he also raised the prospect that the U.N.-sanctioned operation could move beyond the current aerial bombardment if airstrikes fail to topple Gadhafi or bring him to some acceptable accommodation with his armed opponents.

Noting that the U.N. resolution that authorized the attacks prohibits a foreign occupation, Jackson said that doesn’t mean no ground troops. ” ‘Occupation’ is open to interpretation,” he said. “Another interpretation you could make is that limited ground operations could take place.”