AJDABIYA -- Moammar Gadhafi's forces shelled rebels regrouping in the desert dunes outside a strategic eastern city on Tuesday, and his snipers and tanks roamed the streets of the last major opposition-held city in the west, signaling a prolonged battle ahead. An American fighter jet crashed, both crew ejecting safely.

The US Africa Command said both crewmembers were safe in American hands after what was believed to be a mechanical failure of the Air Force F-15 on Monday night. One was picked up by a rebel force and the other by a Marine Corps Osprey search and rescue aircraft.

Disorganization among the rebels could hamper their attempts to exploit the air campaign by US and European militaries, who themselves have struggled to articulate an endgame. Since the uprising began on Feb. 15, the opposition has been made up of disparate groups even as it took control of the entire east of the country.

Regular citizens — residents of the "liberated" areas — formed an enthusiastic but undisciplined force that in the past weeks has charged ahead to fight Gadhafi forces, only to be beaten back by superior firepower. Regular army units that joined the rebellion have proven stronger and more organized, but only a few units have joined the battles while many have stayed behind as officers struggle to get together often antiquated, limited equipment and form a coordinated force.

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The ragtag band of hundreds of fighters who made their way to the outskirts of Ajdabiya on Tuesday milled about, clutching mortars, grenades and assault rifles. Some wore khaki fatigues. One man sported a bright white studded belt.

Some men clambered up power lines in the rolling sand dunes of the desert, squinting and hoping to see Gadhafi's forces inside the besieged city of 140,000 that is the gateway to the east.

"Gadhafi is killing civilians inside Ajdabiya," said Khaled Hamid, a rebel who said he been in Gadhafi's forces but defected to the rebels' side. "Today we will enter Ajdabiya, God willing."

Misrata, the last western city held by rebels, was being bombarded by Gadhafi's forces on Tuesday, his tanks and snipers controlling the streets, according to a doctor there who said civilians were surviving oon dwindling supplies of food and water, desperately in search of shelter.

Speaking on condition of anonymity for fear of reprisals if the city falls to Gadhafi's troops, he accused international forces of failing to protect civilians as promised under the United Nations resolution authorizing military action in Libya.

"Snipers are everywhere in Misrata, shooting any one who walks by while the world is still watching," he said. "The situation is going from bad to worse. We can do nothing but wait. Sometimes we depend on one meal per day."

Mokhtar Ali, a Libyan dissident in exile elsewhere in the Mideast, said he was in touch with his father in Misrata and described increasingly dire conditions.

"Residents live on canned food and rainwater tanks," Ali said. He said Gadhafi's brigades storm residential areas knowing that they won't be bombed there. "People live in total darkness in terms of communications and electricity."

The air campaign by US and European militaries that began Saturday has unquestionably rearranged the map in Libya and rescued rebels from what had appeared to be imminent defeat.

Monday night, Libyan state TV said a new round of strikes had begun in the capital, Tripoli, marking the third night of bombardment. But while the airstrikes can stop Gadhafi's troops from attacking rebel cities — in line with the U.N. mandate to protect civilians — the United States, at least, appeared deeply reluctant to go beyond that toward actively helping the rebel cause to oust the Libyan leader.

US Defense Secretary Robert Gates and others said the US military's role will lessen in coming days as other countries take on more missions and the need declines for large-scale offensive action like the barrage of Tomahawk cruise missiles fired Saturday and Sunday mainly by US ships and submarines off Libya's coast.

A senior defense official, speaking on condition of anonymity to discuss classified data, said Monday that the attacks thus far had reduced Libya's air defense capabilities by more than 50 percent. That has enabled the coalition to focus more on extending the no-fly zone, which is now mainly over the coastal waters off Libya and around the rebel stronghold of Benghazi in the east, across the country to the Tripoli area this week.

In his first public comments on the crisis, Army Gen. Carter Ham, the lead US commander, said it was possible that Gadhafi might manage to retain power.

"I don't think anyone would say that is ideal," the general said Monday, foreseeing a possible outcome that stands in contrast to President Barack Obama's declaration that Gadhafi must go.

The Libyan leader has ruled the North African nation for more than four decades and was a target of American air attacks in 1986.