But greater attention has been focused on a Qaeda involvement in the uprising since mid-July, when fighters professing allegiance to the terrorist organization appeared during the opposition takeover of the Bab al-Hawa border crossing with Turkey. In one video, five fighters declared their intention to create an Islamic state. (Mainline Qaeda ideology calls for a Pan-Islamic caliphate.)

Still, there is, as yet, no significant presence of foreign combatants of any stripe in Syria, fighters and others said. The Saraqib commander estimated there were maybe 50 Qaeda adherents in all of Idlib, a sprawling northwestern province that borders Turkey. The foreigners included Libyans, Algerians and one Spaniard, he said, adding that he much preferred them over homegrown jihadists. They were both less aggressive and less cagey than the locals, said the commander, interviewed in Turkey and via Skype and declining to be further identified.

An activist helping to organize the Syrian military councils said there were roughly 50,000 fighters in total, and far fewer than 1,000 were foreigners, who often have trouble gaining local support. “If there were 10,000, you would know, and less than 1,000 is nothing,” said the activist, Rami, declining for safety reasons to use more than one name.

Not all foreign fighters are jihadists, either. One Libyan-Irish fighter, Mahdi al-Harati, who helped lead the battle for Tripoli, Libya, organized a group of volunteers for Syria, noted Thomas Pierret, a lecturer in contemporary Syrian Islam at the University of Edinburgh. “He is not a jihadi; he sees himself as a Libyan revolutionary there to help the Syrian revolution,” Mr. Pierret said.

Fighters, activists and analysts say that jihadi groups are emerging now for several reasons. They generally stand apart from the Free Syrian Army, the loose national coalition of local militias made up of army defectors and civilian volunteers. Significantly, most of the money flowing to the Syrian opposition is coming from religious donors in Saudi Arabia, Qatar and elsewhere in the Persian Gulf region whose generosity hinges on Salafi teaching.

Further, as the sectarian flavor of the uprising deepened, pitting the majority Sunni Muslims against the ruling minority, the Alawites, it attracted fighters lured by a larger Muslim cause. Alawites, the president’s sect, dominate Syria, but many orthodox Muslims view them as a heretical offshoot of Shiite Islam.

Understanding the military players in the Syrian opposition has become remarkably more difficult in recent months through the proliferation of brigades, battalions and fronts, many bearing religious names. Plus they change all the time, and some have all but disappeared.