By Maria Golovnina and Adrian Croft
TRIPOLI/LONDON (Reuters) - World powers meet on Thursday to try to lay the groundwork for a Libya without Muammar Gaddafi after President Barack Obama said U.S. forces would not get bogged down trying to topple the Libyan leader.
British Prime Minister David Cameron and French President Nicolas Sarkozy, who led the drive for a muscular intervention in the conflict, called on Monday for Gaddafi to go and for his followers to abandon him before it was "too late".
"We call on all Libyans who believe that Gaddafi is leading Libya into a disaster to take the initiative now to organize a transition process," they said in a statement.
Emboldened by Western-led air strikes against Gaddafi's troops, rebels took the town of Nawfaliyah and pushed west toward Sirte, Gaddafi's home town and an important military base, in the sixth week of an uprising against his 41-year rule.
Rebels fired mortars and heavy machineguns in sporadic clashes with loyalist forces in the oil-producing state.
Further west, rebels and forces loyal to Gaddafi both claimed control over parts of Misrata and fighting appeared to persist in the fiercely contested third largest city.
Arab and Libyan media said late on Monday that coalition forces had bombed west and south of the capital Tripoli.
Libyan state television said a leather factory was struck when "colonial and crusader aggressors" bombed Surman, some 70 km (45 miles) west of Tripoli.
The London meeting is expected to set up a high-level steering group, including Arab states, to provide political guidance for the international response to the crisis and coordinate long-term support to Libyans.
Britain has invited Mahmoud Jebril, a member of the rebel Libyan National Council, to London although he is not formally invited to the conference, a diplomatic source said.
Some 40 governments and international organizations will discuss stepping up humanitarian aid, and call for a political process to enable Libyans to choose their own future.
In a nationally televised speech, Obama said NATO would take over full command of military operations from the United States on Wednesday.
Obama vowed to work with allies to hasten Gaddafi's exit from power but said he would not use force to topple him -- as his predecessor President George W. Bush did in ousting Saddam Hussein in the 2003 U.S.-led invasion of Iraq.
"To be blunt, we went down that road in Iraq," Obama told an audience of military officers in Washington. "But regime change there took eight years, thousands of American and Iraqi lives, and nearly a trillion dollars. That is not something we can afford to repeat in Libya."
Broadening the Libya military mission to include regime change would be a mistake, Obama said, and "if we tried to overthrow Gaddafi by force, our coalition would splinter," making it likely U.S. ground troops would have to be deployed.
He did not specify how long U.S. forces would be involved or how they would eventually exit the conflict.
Obama's challenge was to define the limited purpose and scope of the U.S. mission in Libya for Americans preoccupied with domestic economic concerns and weary of costly wars in two other Muslim countries, Iraq and Afghanistan.
Going beyond the specifics of the U.N. resolution that mandated intervention could also risk losing international and Arab support.
Western-led air strikes began on March 19, two days after the U.N. Security Council authorized "all necessary measures" to protect civilians from Gaddafi's forces.
As the diplomatic activity increased ahead of the London conference, Italy proposed a deal including a ceasefire, exile for Gaddafi and dialogue between rebels and tribal leaders.
The rebel leadership has ruled out compromise with Gaddafi's followers.
"We have had a vision from the very beginning and the main ingredient of this vision is the downfall of the Gaddafi regime," spokesman Hafiz Ghoga told reporters in the rebel stronghold of Benghazi in eastern Libya.
Qatar became the first Arab country on Monday to recognize the rebels as the people's legitimate representative, in a move that may presage similar moves from other Gulf states. Libyan state television called the move "blatant interference."
Since the start of the Western-led bombing, the volunteer force of rebels has pressed half-way along the coast from its stronghold of Benghazi toward Tripoli and regained control of major oil terminals in the OPEC state.
The United States has given a green light to sales of crude oil from rebel-held territory, giving a potential boost to the rebels who would not be subject to U.S. sanctions.
But U.S. Vice Admiral Bill Gortney said their battlefield gains in recent days were tenuous.
While the U.S. military is not communicating officially with opposition forces, Gortney said, the United States was seeking to piece together a more complete picture of who they are and where they are positioned.
"We would like a much better understanding of the opposition," he said. "We're trying to fill in those knowledge gaps."
He said the United States had no confirmed report of any civilian casualty caused by coalition forces.
As the rebels pressed on in the east, Gaddafi's troops were patrolling an area near the center of Misrata after shelling the previously rebel-controlled western city for days. The government said it had "liberated" Misrata and declared a ceasefire there.
Gaddafi soldiers manned checkpoints and took up positions on rooftops. Some housefronts were smashed, smoke rose from several areas and gunfire rang out across the city.
Several civilians approached a group of journalists, some of them woman and children waving green flags. "Misrata is ours, there are still some bad guys in other parts, but Gaddafi is winning, the city is ours," resident Abduq Karim said.
Soldiers were manning checkpoints and green Libyan flags flapped in the wind. Militiamen fired AK-47 rifles defiantly into the air. "If they come to Sirte, we will defend our city," said Osama bin Nafaa, 32, a policeman.
(Additional reporting by Angus MacSwan, Alexander Dziadosz, Edmund Blair, Maria Golovnina, Michael Georgy, Ibon Villelabeitia, Lamine Chikhi, Mariam Karouny, Joseph Nasr, Marie-Louise Gumuchian, Steve Gutterman, Matt Spetalnick and Alister Bull; Writing by Alison Williams; Editing by Sanjeev Miglani)