Kaddafi's ground forces have quickly learned that safety from air attack comes in the form of human shields, or just getting into a residential area and some place to hide from the warplanes. But the U.S. sensors are numerous and effective. That, plus the smart bombs, keep the Kaddafi forces vulnerable. The most effective defense is human shields, in the form of any local civilians that can be rounded up. Kaddafi's three most effective brigades are holding together under all this attack, but are shrinking each day from the casualties. Kaddafi troops have, in effect, lost the use of their armored vehicles and artillery. But they can still move safely in the open if they drive civilian vehicles, not in large convoys, and do not communicate on any radio device.
The urban fighting does not benefit much from the NATO air support, mainly because there are few, if any, NATO air controllers down there to call in the extremely precise attacks required in built-up areas. While Kaddafi has thousands of men with military training, and has then formed them into well organized units, the rebels have neither. The rebels are not as united as the Kadaffi forces, and not nearly as effective when attacking (which is always more difficult than defending). Kaddafi troops still have some armored vehicles inside cities like Misarata, which are rolled out when thought safe (from attack) to attack rebel positions, or key sites like hospitals. Kaddafi has his secret police and street gangs in many cities in towns, who are able to harass the rebels, or even defeat them in some places. Kaddafi has cash and lots of promises to give out, and many Libyans with guns will listen.
The war may ultimately be decided by logistics. While the naval and air blockade keeps out new weapons for Kaddafi, that is not a problem for him. He has plenty of stuff already. More importantly, he holds hostage the populations of Tripoli and several other cities. NATO has to let through food and medical supplies, even though the Kaddafi troops and civilian supporters will be at the head of the line for this stuff. Unless NATO imposes a road blockade (no traffic between cities at all), Kaddafi can still move troops via sedan, SUV and van. NATO will not put troops into Libya (aside from the handful of special operations commandos already there), and dealing with the Libyan rebels is like herding cats. Kaddafi believes, with some justification, that he can wait out NATO, and work the sympathy angle via media manipulation.
Kaddafi has time on his side, as the Arab League, after initially backing attacks on him, quickly changed its mind when it saw that this would not be a quick, painless, process. Moreover, most Arab League members are dictators or monarchs, and don't really like the idea of some outsiders (be they the U.S. or the UN), telling them what to do, under the threat of attack.
Over the last five days, the number NATO air sorties over Libya have increased from under a hundred a day to nearly 200. During that same period, the fraction of sorties flown by U.S. aircraft have come to be the majority. This is a problem in the United States, because continuing operations in Iraq and Afghanistan, and a large budget deficit, means it cannot afford to stay involved for long. So, although the U.S. organized the initial attacks, the Americans want someone else to take over command functions and, soon thereafter, provide most of the ships and aircraft. The other NATO nations, accustomed to having the Americans take the lead, and do most of the work, are unsure of how to proceed.
March 22, 2011: A U.S. F-15E fighter-bomber crashes near Benghazi because of equipment failure. Both of the crew bail out safely and are soon picked up by a helicopter from an American carrier off the coast.
March 21, 2011: More NATO warplanes turned their attention to Kaddafi's ground troops, who are laying siege to Ajdabiya in the east and Misarata in the west and advancing on Benghazi. The Libyan coast is largely devoid of cover for columns of trucks and armored vehicles. Despite infrequent contact with rebels forces below, American electronic monitoring aircraft have been able to identify who was below on the highway, and air attacks now go after the columns of Kaddafi troops outside these three cities. This destroys a large chunk of Kaddafi's assault troops.
March 20, 2011: Three American B-2 bombers (flying in from North America) drop concrete penetrating bombs on the fortified aircraft hangers at Libyan airbases. Fifteen U.S. F-15s and F-16s came in from European bases. The U.S. also sent over a dozen aerial refueling and electronic warfare aircraft. The growing NATO fleet offshore was coordinated by a U.S. command ship (designed and equipped for that task.) By the end of the day, NATO believed that Libyan air power and air defenses were largely (but not completely) destroyed. The only anti-aircraft missiles Kaddafi had left were SA-24's (with a max altitude of 3,500 meters/11,000 feet), Russian models similar to the U.S. Stinger.
March 19, 2011: The NATO attack on Kaddafi forces in Libya begin as twenty French warplanes (including an AWACs and several aerial tankers.) Two American destroyers and four nuclear subs (one British) launch 110 cruise missiles towards Libyan targets, mainly air defense radars and missile launchers. Some of these attacks take place after midnight, on the 20th.
March 17, 2011: The UN authorizes "all necessary means" to prevent the forces of Libyan dictator Muamar Kaddafi from killing Libyans. NATO navies had already been moving ships to the Libyan coast, and more are moving in. Italy has an aircraft carrier in the area and the French nuclear carrier the de Gaulle is on the way. Most warplanes are operating from bases in France, Italy and Britain.
March 11, 2011: NATO AWACs aircraft are now monitoring aerial activity over coastal Libya. NATO warships are arriving as well.