* Missiles to be used for defensive purposes - NATO chief
* Heaviest bombardment in Damascus for 40 days - activists
By Angelika Stricker
BRUSSELS, Nov 19 (Reuters) - Turkey is expected to formally request on Monday that advanced NATO Patriot missiles be placed on its border to defend against Syrian attacks, Western officials said.
Syrian rebels fighting President Bashar al-Assad have been able to take large swathes of land but are almost defenceless against Syria's air force. The rebels have called for an internationally enforced no-fly zone, a measure that helped Libyan rebels overthrow their long-term leader last year.
German Defence Minister Thomas de Maiziere said Germany expected Turkey to make the request to NATO for Patriot deployment on Monday and would study such a request "with solidarity".
"But if we have a deployment of Patriots on the Turkish border then this will happen with German soldiers," he told reporters in Brussels, on the sidelines of a meeting of EU defence ministers.
Only the United States, the Netherlands and Germany have the appropriate Patriot missile system available.
NATO Secretary General Anders Fogh Rasmussen said that Turkey could count on "allied solidarity" but said that the missiles would be purely for defence and not for creating a no-fly zone in Syria.
In Damascus, opposition activists said that Assad's forces had started the heaviest bombardment in 40 days of air strikes and artillery shelling aimed at limiting gains by rebels operating on the edge of the capital.
"Multiple rockets launchers are just making huge, random destruction," said Rami al-Sayyed of the Syrian Media Centre, an opposition activists' organisation monitoring Assad's crackdown on the 20-month revolt.
The civil war, which activists say has killed 38,000 people, has dragged Syria's neighbours and world powers into the conflict. Iran, Russia and China have stood by Assad as France, Britain and the United States have called for his overthrow.
Syrian mortar rounds have fallen in Turkey, Lebanon and Israel as rebels hug the borders looking for safety, and Turkey is in talks with NATO allies about how to shore up security on its 900-km (560-mile) frontier.
Turkey's border has witnessed clashes not only between the rebels and Assad's forces but internal rebel disputes and, increasingly, fighting between the rebels and Kurdish separatist groups.
A Reuters cameraman on the Turkish border said that hundreds of families had fled the Syrian town of Ras al-Ain and were gathering at the border gate, after clashes between rebels and Kurdish separatists who are wary of both rebels and the government.
The Turkish army seemed to be on high alert, sending in military jeeps to patrol the border and stationing soldiers in recently dug trenches along the border.
Turkey has responded in kind to Syrian mortar bombs that land on its soil.
NATO has deployed Patriot surface-to-air missiles to Turkey twice before, once in 1991 and then in 2003, during both Gulf Wars. Those missiles were provided by the Netherlands.
Ankara has twice this year invoked Article 4 of the NATO charter which provides for consultations when a member state feels that its territorial integrity, political independence or security is under threat.
Alexander Von Rosenbach, armed forces analyst at IHS Jane's, said deploying Patriots to Turkey would be partly symbolic. "It's more of a commitment from NATO to say we are behind Turkey," he said.
Manufacturer Raytheon says Patriot provides "a reliable and lethal capability to defeat advanced threats, including aircraft, tactical ballistic missiles, cruise missiles and UAVs (drones) ....".