* Qalamoun region is a highly strategic area, near Lebanon

* Highway a likely contender as route for chemical agents

* Locals tell UN 600-800 families fled highway town of Qara

* Chemical watchdog training Syrians to package chemicals

By Oliver Holmes

BEIRUT, Nov 16 (Reuters) - Syrian forces went on the offensive on Saturday against rebels positioned along a major highway linking the capital with the coast, rebels said, a strategic road that is likely to be used to extract chemical weapons from the country.

The road passes through the mountainous area of Qalamoun, roughly 50 km (30 miles) north of Damascus, a region that stretches along the Lebanese border and is one of Syria's most heavily militarised districts.

Captain Islam Alloush, spokesman for the Army of Islam, the largest alliance of rebel groups in the capital, said that fighting was intense in the small highway town of Qara.

"There are a large number of our fighters stationed along the road," he said.

Diplomats say Syrian authorities have identified the road north from Damascus towards Homs and the coast as the preferred route to transport chemical agents under a U.S.-Russian accord to eliminate them from the country's protracted civil war.

Although the army and civilians use the highway, parts of it go near rebel-held areas and convoys are prone to ambushes. The authorities have asked for equipment to help secure convoys.

Observers expect the next big battle in Syria to centre on the Qalamoun area, causing a huge exodus of refugees and stirring up anger in nearby Lebanon as Shi'ite Lebanese Hezbollah fighters take part in the fighting.

The Syrian Observatory for Human Rights, a UK-based monitoring group that uses a network of pro- and anti-Assad sources, said the fighting in Qara and the nearby town of Nabek was "a sign that the operation in Qalamoun has started."

Observatory head Rami Abdelrahman said that Hezbollah militants were mobilising on Saturday to fight in Qalamoun.

United Nations refugee agency spokeswoman Dana Sleiman said there were reports from the Lebanese side of the border that 600-800 refugee families had arrived from Qara at the Lebanese border village of Al-Qaa, escaping the offensive.

STILL TIME

The Organisation for the Prohibition of Chemical Weapons (OPCW) on Friday night adopted a step-by-step plan to get rid of 1,300 tonnes of Syria's sarin, mustard gas and other agents.

The Damascus spokeswoman for the joint OPCW-UN chemical weapons team, Sausan Ghosheh, said the mission would not disclose what route it would use to extract the chemicals but said the "the Syrian authorities have developed a security plan for the transportation of these materials."