* General dropped after moving closer to Qatar
* Saudi-Qatari rivalry in Syria seen behind decision
* Idriss may challenge his sacking, sources say (Adds details, quotes)
By Khaled Yacoub Oweis
AMMAN, Feb 17 (Reuters) - The Western-backed Free Syrian Army (FSA) has sacked its leader after he fell out with the Saudi-supported head of the moderate opposition to President Bashar al-Assad, opposition sources said on Monday.
General Selim Idriss, whose relations with Saudi Arabia deteriorated after he opened channels with Qatar, was replaced by Brigadier General Abdelilah al-Bashir, head of FSA operations in Qunaitera province bordering the Israeli-occupied Golan Heights, the sources said.
Bashir assumes leadership of a force trying to regain the initiative from rival and better organised Islamist groups that have overshadowed it in fighting against Assad.
A statement signed by 22 of the FSA's 30-member Supreme Military Council said the decision was prompted by "the ineffectiveness of the command in the past few months... and to provide leadership for military operations against the criminal regime and its allies from terrorist organisations."
A statement by the opposition National Coalition, which includes 15 members of the FSA, said news of Bashir's appointment came as a "relief".
Ahmad Jarba, a tribal figure close to Saudi Arabia, became president of the coalition last July after an expansion last year that diluted the influence of Qatari-backed members.
"Idriss appears to have gotten too close to the Qataris, prompting Jarba to move against him," one of the opposition sources said.
Rivalry between Saudi Arabia and Qatar, main backers of Assad's civilian and military opponents, has deepened divisions in the opposition. It has also strengthened Assad as his government talks with the opposition National Coalition at U.S.-and Russian-sponsored negotiations in Geneva.
The coalition's delegation added several FSA commanders to its negotiating team in the second round of peace talks, which concluded on the weekend without any significant results.
The announcement to remove Idriss, who had served in the Corps of Engineers of Assad's army, was made on Sunday after a Supreme Military Council meeting in Turkey attended by Asaad Mustafa, defence minister in a provisional government set up by the opposition last year, the sources said.
Mustafa, whose relations with Idriss have been tense, indicated last week to members of the provisional government that he intended to resign. He changed his mind after receiving political backing from Jarba, an official in the opposition government said.
Idriss was visiting the United Arab Emirates when he learned of his sacking, the sources said. He still has supporters in the FSA's Supreme Military Council and could try to contest the decision with their help.
IDRISS STILL HAS SUPPORT
Dissident rebels have long been wary of accepting Idriss, who has spent most of his time outside Syria since being chosen as a consensus figure to lead the Supreme Military Council set up with Arab and Western backing in Turkey in Dec. 2012.
But a diplomat based in the Middle East said Bashir, Idriss' replacement, is a relative unknown who is unlikely to solve divisions within the FSA.
"Idriss supporters are not going to take his sacking sitting down. The only reason Bashir was appointed is that he is close to Jarba," the diplomat said.
The FSA has suffered major setbacks since initial advances against Assad two years ago.
Loyalist forces backed by Shi'ite fighters from Iran, Iraq and Lebanon's Hezbollah regained strategic territory in the province of Homs and expanded a buffer zone around Damascus, where most elite troops, mostly comprised of Assad's minority Alawite sect, are based.
Al-Qaeda-linked groups also emerged as a potent force on the ground, and several Islamist brigades broke off from the FSA, helping create the Islamic Rebel Front, which overshadowed the FSA militarily. (Editing by Tom Heneghan)