He said he is frustrated at times with the lack of discipline among the rebels, the vast majority of them civilians without proper military training.
"We need a lot of patience," he said. "If we have a battle, some show up without invitation. They want to take part and shoot."
Idris said that on Tuesday, he spent much the day near the central city of Hama, observing a successful rebel attempt to capture five regime checkpoints.
Syria's conflict began with a popular uprising in March 2011, but quickly turned violent, with protesters taking up arms in response to a brutal regime crackdown. Activists say more than 40,000 Syrians have been killed and aid officials estimate some 3 million people have been displaced by the fighting.
Idris portrayed Assad as a powerless figurehead, saying decisions are made by his inner circle of fellow Alawites, followers of an offshoot of Shiite Islam and a minority in Syria. The opposition is dominated by majority Sunni Muslims.
The ruling elite won't surrender and is willing "to set everything on fire," warned Idris, who served in the military for 35 years, including as dean at the military's technical college in the city of Aleppo, now a major battleground.
U.S. officials have said the Syrian regime launched more than a half-dozen Scud missiles in recent days, the first time it has used such weapons in this conflict. Idris said he was aware of three launches, including two missiles that fell in Syria's eastern desert and a third on the outskirts of a town close to Aleppo.
Idris, citing information from rebel sympathizers within the regime, said Scud missiles are being trained at northwestern Syria, the area close to the Turkish border, and could be fired at any moment.