By Suleiman Al-Khalidi, Maya Gebeily and Khalil Ashawi

AMMAN/BEIRUT/DAMASCUS (Reuters) - Syria's transitional President Ahmed al-Sharaa and Turkish President Tayyip Erdogan are expected to discuss a joint defense pact in Ankara on Tuesday, including establishing Turkish airbases in central Syria and training for Syria's new army, four sources familiar with the matter said.

NATO member Turkey has long backed Syria's armed and political opposition to ousted leader Bashar al-Assad, who was toppled in late December in a lightning offensive spearheaded by Sharaa's forces.

Ankara is positioning itself to play a major role in the new Syria, filling a vacuum left by Assad's main regional backer Iran, in an expansion of Turkish sway that could spark rivalry with Gulf Arab states and put Israel on edge.  

The sources - a Syrian security official, two Damascus-based foreign security sources and a senior regional intelligence official - spoke on condition of anonymity as they were not authorised to speak to the media about the meeting.

This is the first time that elements of any strategic defense arrangement by Syria's new leaders, including details of additional Turkish bases, have come to light.

The pact could see Turkey establish new air bases in Syria, use Syrian airspace for military purposes, and take a lead role in training troops in Syria's new army, the sources said.

Syria's new leadership has dissolved the army and its various rebel factions, and is working on integrating them into a new military command.

The sources said the deal was not expected to be finalised on Tuesday.

TURKISH AIR BASES IN SYRIA

The regional intelligence official, the Syrian security official and one of the Damascus-based foreign security sources said the talks would include setting up two Turkish bases in Syria's vast central desert region, known as the Badiyah.

An official in Syria's presidency told Reuters that Sharaa would discuss Turkey's "training of the new Syrian army, as well as new areas of deployment and cooperation" with Erdogan, without specifying the deployment locations.

The Turkish presidency and Syrian defense ministry did not immediately respond to a request for comment on the issue.

The Turkish presidency's communications director Fahrettin Altun said on Monday that Erdogan and Sharaa would discuss the latest developments in Syria and possible joint measures to rebuild Syria's economy and achieve stability and security.

A Turkish defence ministry official familiar with the talks between both defence ministries told Reuters he did not have information on Turkish bases in Syria and training for Syrian troops as part of a possible defence pact.

TURKEY'S AIR DEFENSE ROLE

The senior regional intelligence official, the Syrian security official and one of the Damascus-based foreign security sources said the bases under discussion would allow Turkey to defend Syria's air space in case of any future attacks.

Assad's other main backer - Russia - is also in talks with the new Damascus administration about the fate of its two military bases in Syria, a naval base in Tartous and an air base near the port city of Latakia, the Kremlin said on Monday.

In an interview in January, Syria's defense minister Murhaf Abu Qasra told Reuters the country's new leaders would seek to build strong ties in the region, "and that through these ties, we will be able to build our military force well."

If these ties lead to a partnership "on arming, training, air defense or other issues - we would welcome it," Abu Qasra said, without mentioning Turkey.

The regional intelligence official said the possible airbase locations were the Palmyra military airport and the Syrian army's T4 base, both in the province of Homs.

MESSAGE TO KURDISH FIGHTERS

The official said Ankara was keen to set up bases there as a message to Kurdish fighters in northeast Syria, known as the People's Protection Units (YPG).

Ankara views them as an extension of the Kurdistan Workers Party (PKK), which has been waging an insurgency against the Turkish state since 1984 and is deemed a terrorist group by both Turkey and the U.S.

Turkey has threatened a military offensive against the YPG, but has held off as talks are underway to address the fate of the Kurdish forces.

The Turkish defense ministry official told Reuters that Turkish and Syrian military delegations exchanged views last week on "what can be done in defence and security matters, especially in the joint fight against terrorist organizations that pose a threat to both Syria and Turkey."

"Our meetings will continue within the framework of the needs that will occur in coming period," the official added.

Turkish Defence Minister Yasar Guler said in December that Turkey was "ready to provide the necessary support if the new (Syrian) administration requested it.

Ankara may discuss and reevaluate the issue of Turkey's military presence in Syria with the new Syrian administration "when necessary conditions arise," Guler said at the time.

(Reporting by Suleiman al-Khalidi in Amman, Maya Gebeily in Beirut, Khalil Ashawi in Damascus and Huseyin Hayatsever in Ankara; Editing by Bernadette Baum)