* Lebanese pro-Syrian source talks of optimism in Damascus
* Wary opposition says no deal can leave Assad in power
* Artillery attack kills 20 in northern village
* Video shows dozens of Assad fighters dead on roadside
* 120 Syrians killed so far on Wednesday-activists
By Erika Solomon
BEIRUT, Dec 26 (Reuters) - Syrian President Bashar al-Assad sent a senior diplomat to Moscow on Wednesday to discuss proposals to end the conflict convulsing his country made by international envoy Lakhdar Brahimi, Syrian and Lebanese sources said.
Brahimi, who saw Assad on Monday and is planning to hold a series of meetings with Syrian officials and dissidents in Damascus this week, is trying to broker a peaceful transfer of power, but has disclosed little about how this might be done.
More than 44,000 Syrians have been killed in a revolt against four decades of Assad family rule, a conflict that began with peaceful protests in March last year, but which has descended into civil war.
A video posted by rebels on Wednesday showed the bodies of dozens of soldiers executed by a roadside. At least one of them apeared to have been beaten to death. The United Nations and rights group say the military and rebels have both committed war crimes, but have so far placed most of the blame on the army.
Past peace efforts have floundered, with world powers divided over what has become an increasingly sectarian struggle between mostly Sunni Muslim rebels and Assad's security forces, drawn primarily from his Shi'ite-rooted Alawite minority.
Deputy Foreign Minister Faisal Makdad flew to Moscow to discuss the details of the talks with Brahimi, said a Syrian security source, who would not say if a deal was in the works.
However, a Lebanese official close to Damascus said Makdad had been sent to seek Russian advice on a possible agreement.
He said Syrian officials were upbeat after talks with Brahimi, the U.N.-Arab League envoy, who met Foreign Minister Walid Moualem on Tuesday a day after his session with Assad, but who has not outlined his ideas in public.
"There is a new mood now and something good is happening," the official said, asking not to be named. He gave no details.
Russia, which has given Assad diplomatic and military aid to help him weather the 21-month-old uprising, has said it is not protecting him, but has fiercely criticised any foreign backing for rebels and, with China, has blocked U.N. Security Council action on Syria.
SEEKING A SETTLEMENT
A Russian Foreign Ministry source said Makdad and an aide would meet Foreign Minister Sergei Lavrov and Mikhail Bogdanov, the Kremlin's special envoy for Middle East affairs, on Thursday, but did not disclose the nature of the talks.
On Saturday, Lavrov said Syria's civil war had reached a stalemate, saying international efforts to get Assad to quit would fail. Bogdanov had earlier acknowledged that Syrian rebels were gaining ground and might win.
Given the scale of the bloodshed and destruction, Assad's opponents insist the Syrian president must go.
Moaz Alkhatib, head of the internationally-recognised Syrian National Coalition opposition, has criticised any notion of a transitional government in which Assad would stay on as a figurehead president stripped of real powers.
Comments on Alkhatib's Facebook page on Monday suggested that the opposition believed this was one of Brahimi's ideas.
"The government and its president cannot stay in power, with or without their powers," Alkhatib wrote, saying his Coalition had told Brahimi it rejected any such solution.
While Brahimi was working to bridge the vast gaps between Assad and his foes, fighting raged across the country and a senior Syrian military officer defected to the rebels.
In the northern province of al-Raqqa, Syrian army shelling killed about 20 people, at least eight of them children, a video posted by opposition campaigners showed.
The video, uploaded by the Syrian Observatory for Human Rights, showed rows of blood-stained bodies laid out on blankets. Sobbing relatives could be heard in the background.
The shelling hit the province's al-Qahtania village early on Wednesday. The British-based Observatory, which has a network of activists across Syria, said there was no rebel presence in the town, and the motives of the attack were unclear.
"THIS IS THE FATE OF SWINE"
As the violence grows, so does sectarian-infused hatred between the Sunni Muslim majority and minorities such as Assad's Alawite sect, which has largely supported the president.
Several Islamist units, among them the U.S. blacklisted Jabhat al-Nusra, released a video showing the bodies of dozens of Assad's fighters along a highway near an Alawite town in the central province of Hama, where rebels launched a new offensive.
The unseen speaker in the video dated the scene to Dec. 21 and said 50 men were ambushed in a convoy and killed. Piles of bodies lined the road with many more scattered further away. One of the men appeared to have been beaten to death, with parts of his face smashed in and some of the skull protruding.
"Let this be a lesson," the cameraman says. "These are Assad's apostate dogs on the road ... this is the fate of all swine."
On the back of the Hama offensive, rebels relaunched their assault on the Wadi Deif military base in the northwestern province of Idlib, in a battle for a major army compound and fuel storage and distribution point.
The military used artillery and air strikes to try to hold back rebels assaulting Wadi Deif and the town of Morek in Hama province further south, where they have cut its supply routes. In one air raid, rockets fell near a field hospital in Idlib's town of Saraqeb, wounding several people, the Observatory said.
As violence has intensified in recent weeks, the death toll has climbed. The Observatory reported at least 120 killed across the country on Wednesday, a number likely to rise overnight.
The head of Syria's military police changed sides and declared allegiance to the anti-Assad revolt.
"I am General Abdelaziz Jassim al-Shalal, head of the military police. I have defected because of the deviation of the army from its primary duty of protecting the country and its transformation into gangs of killing and destruction," the officer said in a video published on YouTube.
A Syrian security source confirmed the defection, but said Shalal was near retirement and had only defected to "play hero".