* Government troops attack Misrata
* Rebels pushed back in the east
(Updates with Arab League decision)
By Michael Georgy and Yasmine Saleh
RAS LANUF, Libya/CAIRO March 12 (Reuters) - Arab countries appealed to the United Nations to impose a no-fly zone on Libya as pro-government troops backed by warplanes fought to drive rebels from remaining strongholds in the west of the country.
Arab League Secretary General Amr Moussa said the League, meeting in Cairo on Saturday, had decided that "serious crimes and great violations" committed by the government of Muammar Gaddafi against his people had stripped it of legitimacy.
The League's call for a no-fly zone could provide the regional endorsement that NATO has said is needed for any military action to curb Gaddafi. The League also said it had opened contacts with the Libyan rebel leadership.
Events on the ground, however, are moving more quickly than international diplomatic efforts. The EU and the United States have both balked at proposing a no-fly zone as Gaddafi steps up his effort to crush the uprising against his four-decade rule.
Pro-Gaddafi troops unleashed an assault on the town of Misrata, the only rebel outpost between the capital and the eastern front around the oil town of Ras Lanuf.
"We are hearing shelling. We have no choice but to fight," rebel spokesman Gemal said by telephone from Misrata. "I can hear loud explosions," said a resident who would only give his name as Mohammad. "Everybody is rushing home, the shops have closed and the rebels are taking up positions."
Mussa Ibrahim, a government spokesman in Tripoli, could neither confirm nor deny a military operation was under way.
"There is a hard core of al Qaeda fighters there," he said. "It looks like a Zawiyah scenario. Some people will give up, some will disappear ... Tribal leaders are talking to them. Those who stay behind, we will deal with them accordingly."
It took a week of repeated assaults by government troops, backed by tanks and air power, to crush the uprising in Zawiyah, a much smaller town 50 km (30 miles) west of Tripoli.
While the death toll in Zawiyah is unknown, much of the town was destroyed, with buildings around the main square showing gaping holes blown by tank rounds and rockets. Gaddafi's forces bulldozed a cemetery where rebel fighters had been buried.
"BRACING FOR A MASSACRE"
Gaddafi's guns are now trained on Misrata. "We are bracing for a massacre," said Mohammad Ahmed, a rebel fighter. "We know it will happen and Misrata will be like Zawiyah, but we believe in God. We do not have the capabilities to fight Gaddafi and his forces. They have tanks and heavy weapons and we have our belief and trust in God."
Further east, Gaddafi's troops pushed insurgents out of Ras Lanuf, a day after making an amphibious assault on the oil port and pitting tanks and jets against rebels armed with light weapons and machineguns mounted on pick-up trucks.
Libyan troops were waving posters of Gaddafi and painting over rebel graffiti in Ras Lanuf later in the day when foreign journalists arrived on an official visit.
Libya's flat desert terrain favours the use of heavy armour and air power. The Libyan army is also better trained and more disciplined than the rag-tag, though enthusiastic, rebel force.
The rebels have repeatedly called for foreign countries to impose a no-fly zone to stop air strikes on cities, while insisting they do not want military intervention on the ground.
Arab League Secretary General Moussa told a news conference after Cairo talks: "The Arab League has officially requested the U.N. Security Council to impose a no-fly zone against any military action against the Libyan people."
It was not immediately clear how Russia and China, who have veto rights in the Security Council and have publicly opposed a no-fly zone, would react to a call for action from a regional body; the more so since the call was, according to Omani Foreign Minister Youssef bin Alawi bin Abdullah, backed unanimously.
The terms of any no-fly zone would have to be agreed carefully and time may be working against the rebels. Its general aim would be to stop Gaddafi using his air force in attacking rebel forces, transport and reconnaissance.
President Barack Obama said the United States and its allies were "tightening the noose" on Gaddafi and that he had not taken any options off the table, a hint at military action. But there is little enthusiasm in Washington for enforcing a no-fly zone without United Nations backing.
European Union leaders meeting in Brussels on Friday sidestepped a British and French call to draw up a U.N. Security Council resolution to authorise a no-fly zone over Libya. Instead, they called for a three-way summit with the African Union and the Arab League to discuss the crisis further.
Western states' reluctance to intervene in an Arab conflict, amid pleas from the rebels and now the League, might win them few friends in a Middle East now in a period of transformation. "The risks of intervening are great. But the Arabs in revolt share a fundamental value with people in the West -- the call of freedom. Whoever does not honour this debt will find himself, five or six years from now, back sitting with Gaddafi in his Bedouin tent," wrote Tomas Avenarius in the German Sueddeutsche Zeitung.
"If Gaddafi goes on slaughtering his people, the Americans and Europeans will have to get involved in the end. Their own claims to morality and the calls from supporters of human rights ... will not let thousands die in Libya while politicians look on idly from the far side of the Mediterranean." Ahmed, a rebel fighter in Misrata, said: "The fighters here and the people of Misrata hold the international community responsible for the fall of Zawiyah and for all the deaths that happened. Gaddafi is responsible, but they are partners in crime.
"They do not care for us. All they care for is the oil, and it seems they are waiting to see who is going to win so that they can deal with them, whether it's Gaddafi or us. They do not want to burn their bridges with him. All they do is say they are assessing the situation. Why are they taking so long?"
(Additional reporting by Maria Golovnina in Zawiyah, Mohammed Abbas in Brega, Tom Pfeiffer in Benghazi, Mariam Karouny in Ras Jdir, Tunisia, Writing by Jon Hemming and Ralph Boulton; Editing by Kevin Liffey)