By Emma Farge

LONDON (Reuters) - Pro-Gaddafi fighters may resort to hit-and-run guerilla attacks against Libyan politicians, foreign workers and oil installations in the remote southwestern Fezzan district if they are driven from their last bastions, risk consultants say.

A full-scale insurgency like the one that erupted in Iraq following the ouster of Saddam Hussein by U.S.-led forces is unlikely, but a determined guerrilla campaign could make life difficult for Libya's new rulers and foreign oil companies considering a return.

"Gaddafi supporters will not be able to conduct an insurgency because they do not have the popular support, but they have the technical ability to launch a bombing and assassination campaign against foreigners and NTC leaders," said Firas Abi Ali, deputy head of Middle East and North Africa forecasting for Exclusive Analysis.

Forces loyal to Libya's ruling National Transitional Council are now moving more tanks into the center of Sirte to try to crush the last pocket of resistance by loyalists of ousted leader Muammar Gaddafi in his home town. Other loyalists are still holding out in Bani Walid.

But guerrilla tactics, used throughout Libyan history against colonial rulers, could stall efforts to rebuild the country after eight months of fighting and ward off foreign oil workers, who are seen as key to restoring output to pre-war levels of 1.6 million barrels per day.

Such a strategy would also complicate decisions for foreign airlines and oil companies torn between returning to business and protecting their staff in the heavily-armed and heavily-mined country.

Many are for now settling for quick meet-and-greet encounters with Libya's new leaders in Tripoli until they get further assurances on safety.

Control Risks last week dropped its assessment of the travel risk to Tripoli to "high" but the classification remains "extreme" in many other parts of the country.

But that was before a gunbattle erupted in the Libyan capital on Friday between NTC forces and up to 50 armed supporters of the deposed Gaddafi.

Even for those who think the gains justify the risks, insurance premiums are high for doing business in a country where NATO has vowed to extend an air-and-sea campaign until at least December.

FEZZAN ACHILLES' HEEL

Analysts said that the highest-risk area for attacks was in the oil-rich southwestern Saharan desert region, Fezzan, which was held by pro-Gaddafi fighters until late September.

Fezzan, where many Libyans believe their former leader is in hiding, is home to Eni's Elephant and Repsol's Sharara fields. Their combined capacity of around 330,000 bpd is about a fifth of Libya's total pre-war output.

While the impact on the oil industry in this region would be less than in the Sirte Basin, now deemed to be relatively secure, attacks could still slow or even halt the ramp-up in oil production keenly awaited by cash-strapped Libyan leaders and consumer countries alike.

Control Risk's Henry Smith said installations in the remote Fezzan region were an easy target for roaming militia who could strike, then swiftly disappear back into the desert.

"The most significant security threats to oil assets are in the Ubari sand sea, broadly between Ghadames, Sabha and Ghat. It is not secure and anyone who has been there will tell you it will remain difficult to police, particularly given the lack of a central security force," he said.

Oil facilities have already been attacked by pro-Gaddafi forces this summer, and in September the Ras Lanuf refinery and export terminal in eastern Libya was ambushed and 17 killed despite being behind NTC lines and supposedly protected by the eastern brigades.

"There's a high risk of hit-and-run attacks on oil workers, blowing up pumping stations or shooting down aircraft that carry people and equipment to fields in the Ubari and Murzuq basins," said Firas Abi Ali, referring to parts of southwest Libya.

WEAPONS BOUNTY

Both consultants warned that the risk was higher because of the number of unsecured weapons in the country left over from the conflict, including anti-aircraft missiles.

Turkish Airlines has resumed commercial flights to Libya despite the no-fly but other carriers have been more cautious. British Airways, for instance saying it would not resume operations before a NATO no-fly zone was lifted.

Even some Libyan oil workers are apprehensive about returning to desert oilfields after some of the facilities were sabotaged by militia.

"If they find out people are here they might come back," said an oilfield manager in the region.

(Reporting by Emma Farge; Additional reporting by Jessica Donati and Dmitry Zhdannikov; Editing by Jon Boyle)