In recent weeks, rebel groups have been killing one another with increasing ferocity, losing ground on the battlefield and alienating the very citizens they say they want to liberate. At the same time, the United States and other Western powers that have called for Mr. Assad to step down have shown new reluctance to provide the rebels with badly needed weapons.

Although few expect that Mr. Assad can reassert his authority over the whole of Syria, even some of his staunchest enemies acknowledge that his position is stronger than it has been in months. His resilience suggests that he has carved out what amounts to a rump state in central Syria that is firmly backed by Russia, Iran and Hezbollah and that Mr. Assad and his supporters will probably continue to chip away at the splintered rebel movement.

“Assad is powerful now, not as a president who controls a state but as a warlord, as someone who has more and more sophisticated weapons than the others,” said Hassan Hassan, a Syrian commentator at the Abu Dhabi-based English-language newspaper The National. “He is not capable of winning back the country.”…

“If the revolution continues like this, the people will revolt against us,” said a rebel commander from the central city of Homs, where Mr. Assad’s forces have made gains in recent days.