* Syria's deputy foreign minister heads to Moscow
* 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
Syrian President Bashar al-Assad despatched a senior diplomat to Moscow on Wednesday to discuss proposals made by envoy Lakhdar Brahimi to end the conflict convulsing his country, Syrian and Lebanese sources said.
Brahimi, who met Assad on Monday as part of a series of planned talks with Syrian officials and dissidents in Damascus this week, is trying to arrange a peaceful transfer of power, but has disclosed little about how this might be achieved.
More than 44,000 Syrians have died in the revolt against four decades of Assad family rule, a conflict that began with peaceful protests but which has descended into civil war.
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 in 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.
On Saturday, Russian Foreign Minister Sergei Lavrov said Syria's civil war had reached stalemate and international efforts to persuade Assad to quit would fail.
Assad's opponents insist the Syrian president must go, given the scale of bloodshed and destruction they blame on him.
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 any real powers.
SHELLING KILLS 20
The comments on Alkhatib's Facebook page on Monday suggested that the opposition believed this was among Brahimi's ideas.
"We have told every official we have met: the government and its president cannot stay on in power, with or without their powers. This is unacceptable to Syrians," Alkhatib wrote.
"The coalition leadership has told Lakhdar Brahimi directly that this type of solution is rejected."
While Brahimi was striving to bridge the vast gaps between Assad and his foes, fighting raged on across the country and a senior Syrian military officer defected to the rebels.
Syrian army shelling killed about 20 people, at least eight of them children, in the northern province of Raqqa, a video posted by opposition campaigners showed.
The video published by the Syrian Observatory for Human Rights showed rows of blood-stained bodies laid out on blankets. The sound of crying relatives could be heard in the background.
The shelling hit the province's al-Qahtania village, but it was unclear when the attack had occurred.
Rebels re-launched their assault on the Wadi Deif military base in the northwestern province of Idlib, in a critical battle for a major army base and fuel storage and distribution point.
Activist Ahmed Kaddour said rebels were firing mortars and had attacked the base with an explosives-rigged vehicle.
The British-based Observatory, which uses a network of contacts in Syria to monitor the conflict, said a rebel commander was among several killed in Wednesday's fighting, which it said was among the heaviest there for months.
As violence has intensified in recent weeks, with Assad using his air power and artillery to contain rebel advances, daily death tolls have climbed. At least 190 were killed across the country on Tuesday alone, the Observatory said.
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".
Syrian Interior Minister Mohammed Ibrahim al-Shaar left Lebanon for Damascus after being treated in Beirut for wounds sustained in a rebel bomb attack this month.