In a meeting with reporters at the Pentagon Tuesday, Gates said no further decisions have been made on potential missions in Libya. He noted that a U.N. Security Council resolution does not contain authorization for any military operations.

None of the U.S. planners involved will talk on the record. Privately, though, planners, strategists and analysts describe a range of potential missions from imposing "no-fly'' and "no-drive'' zones (to prevent the movement of Gadhafi's security forces) to launching limited and short-duration humanitarian relief operations. And because operations planners must consider worst-case situations, some also are looking at larger-scale armed intervention. Preferably, U.S.officials said, any U.S. intervention would take place under United Nations auspices and be undertaken jointly with NATO allies and others.

But while the necessary work is underway of planning what would be complex military operations, there is a sense that the conflict in Libya will unfold on its own.

"I don't see a military mission," said Robert Killebrew, a retired Army strategic planner. "It would be one thing if there were Americans being held hostage. Then we have to intervene. Barring that, it's unclear what the military would do." Killebrew is now a senior analyst at the Center for a New American Security, a Washington think tank.

The risk of U.S. military involvement is reflected in a variant of Colin Powell's "Pottery Barn rule." As the former four-star general and then-secretary of state warned President Bush in 2002, regarding an invasion of Iraq, "You break it, you own it."

By intervening in Libya, "the United States and its allies might find themselves in the position of midwifing a bad outcome if the situation degenerated into civil war or chaotic violence, or if radical Islamist elements gained power," write Jason Hanover and Jeffrey White of the Washington Institute on Near East Policy.

And there is the precedent of Somalia, where a well-intentioned impulse to "do something" turned into a deadly rout. In August 1992, President George H.W. Bush authorized the military to begin flying food shipments into drought-stricken Somalia. But supply convoys run by relief organizations came under attack by local gangs, which hijacked the food for resale on the open market. By December, Bush -- who had lost his reelection bid to Bill Clinton -- came under pressure to protect the convoys, and sent in Marines and troops of the 10^th Mountain Division, a force that reached upwards of 10,000 assigned to work with international troops under a U.N. mandate.

Operation Restore Hope grew into a series of deadly clashes with Somali gangs and, it turned out, elements of early al-Qaeda units. Under the U.N. mandate, American troops had no authority to disarm the gangs, and the fighting escalated to the deadly October 1993 firefight portrayed in the book "Blackhawk Down."

U.S. forces were withdrawn, with the last troops being evacuated by sea the following March. As they withdrew, mobs stormed the American embassy building, which had recently been expanded.

The debacle soured many on the idea of peacekeeping in a chaotic situation where local government authority had broken down. An official Army history of Restore Hope concluded: "The American soldier had, as always, done his best under difficult circumstances to perform a complex and often confusing mission. But the best soldiers in the world can only lay the foundation for peace; they cannot create peace itself."

Libya, of course, is not Somalia. Rather than an ungoverned territory fought over by rival gangs and warlords, Libya is a settled, developed country that presents its own complications to military planners. Among them:

-- A no-fly zone, patrolled by U.S. and European aircraft, would be extremely complex, requiring coordination with a rotation of aerial refueling tankers, and strike fighters poised against Gadhafi's surface-to-air missile batteries. Even if tightly enforced, a no-fly zone would have little or no impact on the outcome of the struggle on the ground, analysts say. Gadhafi has occasionally used strike fighters from his decrepit air force against rebel forces to little evident effect, while the struggle on the ground has continued unabated.

-- A "no-drive" zone, designed to prevent Gadhafi from using his ground forces, would have to be enforced by aircraft. U.S. JSTARS aircraft could track moving vehicles with ease -- but could not tell whether vehicles were occupied by anti-Gadhafi forces or pro-Gadhafi forces. That raises the potential for mistakenly killing pro-democracy protesters.

-- Humanitarian intervention: The 26^th MEU aboard the USS Kearsarge has the equipment and the training to evacuate civilians from shore and temporarily treat as many as 600 injured civilians in its hospital bays. It could easily land several hundred Marines to provide security and other support for civilian humanitarian organizations helping to feed and house refugees. But as the Somalia precedent suggests, such armed intervention, even if initially limited in scope, can easily expand.

U.S. forces can overcome such problems, of course. But any military option, analysts stress, carries with it enormous uncertainties.

"Libyans in my opinion have to do this for themselves," said Killebrew. "They will eventually kick Gadhafi out. Rebels want to fight their own war, and for us to intervene in a family fight is always a scary thing to do."