Obama must navigate rival agendas from the international coalition flying through Libyan skies. Is the mission to stop Qaddafi from harming civilians or to compel his surrender?

Libyan rebels patrol the center of Benghazi, eastern Libya, Sunday, March 20, 2011. AP.

And so it begins, with explosions lighting up the Libyan sky. But the allied campaign against Muammar Qaddafi doesn't answer the most basic question of all: What exactly is the objective?

Strategy is about using our capabilities to achieve well-defined aims. But in the Libyan operation, there's little clarity over the objectives. Some members of the alliance see the military as a shield to protect civilians; others view it as a sword to topple Qaddafi's regime. The first aim is defensive; the second is offensive. The first mission is to stop Qaddafi from harming civilians; the second is to compel his surrender. 

Caught between these rival agendas, Obama must navigate the shoals of Tripoli.

Different objectives call for different tactics. If we're trying to alleviate suffering, we need to negotiate with Tripoli. But if we demand unconditional surrender, there's little point in talking.

On one side of the coalition are the cautious warriors who view the intervening forces as a shield. This is a limited operation with narrow humanitarian goals: to degrade Qaddafi's ability to target civilians, and deter him from further atrocities.

According to UN Security Council Resolution 1973, the operation will "protect civilians and civilian-populated areas under threat of attack in the Libyan Arab Jamahiriya, including Benghazi, while excluding a foreign occupation force of any form on any part of Libyan territory."

The Secretary General of the Arab League, Amr Moussa, saw allied intervention as defensive: "The goal is to protect civilians first of all, and not to invade or occupy."

Similarly, the Chairman of the Joint Chiefs of Staff Mike Mullen claimed that the campaign could be a success even if Qaddafi remains in office: "the goals of this campaign right now are limited, and it isn't about seeing him go."

On the other side of the coalition are those who view the military as a sword to overthrow the tyrant. The UN resolution may prohibit an occupying army, but it also gives wide latitude to strike Qaddafi. Force can be used to protect "civilians" and also "civilian-populated areas under threat of attack"--virtually a blank check to attack the regime's military.

The French are firmly in the hawkish camp. Paris has already given diplomatic recognition to the Libyan rebels. One French government spokesman said that air strikes would "allow [the Libyan people] to go all the way in their drive, which means bringing down the Qaddafi regime." Meanwhile, British Prime Minister David Cameron claimed that Qaddafi "needs to go."

Secretary of State Hillary Clinton also used tough language: "if you don't get him [Qaddafi] out and if you don't support the opposition and he stays in power, there's no telling what he will do."

Meanwhile, Obama seems to be hedging his bets. The president avoided setting the target sights on Qaddafi, and described a "focused" mission to aid civilians. But Obama also said the Libyan dictator had lost "the legitimacy to lead" and must comply with far-reaching demands, including a ceasefire and a withdrawal of forces from Ajdabiya, Misrata, and Zawiya.

These divisions over war aims are not easy to paper over. After all, different objectives call for different tactics. If we're trying to alleviate suffering, we need to negotiate with Tripoli. But if we demand unconditional surrender, there's little point in talking.

The scope and difficulty of the missions also vary dramatically. We can readily stop the regime from conquering Benghazi--although this will hardly resolve the Libyan civil war.

But it's not at all clear how we achieve regime change. The UN resolution forbids an occupying army, and Obama has taken American ground forces off the table. The French called for the Libyan people to bring down the government. But we waited to act until Qaddafi had driven the rebels back to the gates of Benghazi. Now the rebels need to fight their way across North Africa again. Even with allied air cover, it could be a long road to victory.

The ties binding the alliance together could fray or break, undermining the war effort. Already, the head of the Arab League has reportedly condemned allied air strikes that killed Libyan civilians: "What is happening in Libya differs from the aim of imposing a no-fly zone, and what we want is the protection of civilians and not the bombardment of more civilians."

It will take all of Obama's political skill to resolve these tensions and prevent Qaddafi from driving a wedge between the allies so he can finish off the rebels.