Continued from page 1

“You see a strategic shift in which the rebels are now actively targeting the regime’s supply lines and air bases as a way to limit its effectiveness in the air, which is the rebels’ biggest weakness,” said Elizabeth O’Bagy, a research analyst at the Institute for the Study of War.

The rebels have seized enough arms and ammunition from the bases to last for a month of fighting in the north, according to multiple rebel sources inside Syria who spoke on background.

Despite these setbacks, the regime still has plenty of firepower. In Damascus, Mr. Assad has two military divisions that are largely intact and have not seen much fighting.

“For what it’s worth, the regime still has a significant arsenal,” said Ms. O’Bagy. “It is premature to say the regime is on its last legs. In areas where the regime has strategic interests, it can continue to defeat the rebel offensive.”

She said the only way the rebels will be able to take over the cities and notch up strategic victories is if they get a substantial boost in weapons capability and training. The rebels have received arms from their Persian Gulf allies. However, the United States has been reluctant to provide weapons out of concern that they will fall into the hands of Islamic extremists.

The resistance suffered a setback this week when the State Department designated the rebel group, Jabhat Nusra, as an al Qaeda front and a foreign terrorist organization. The group is widely acknowledged as one of the more effective and better organized rebel units fighting the Assad regime.

“Even the moderates in the Syrian national coalition recognize that Jabhat Nusra is the most important fighting force on the ground,” said Ms. Ottaway.

Syrian opposition leader Mouaz Alkhatib on Wednesday urged the Obama administration to reconsider its designation of Jabhat Nusra as a terrorist organization.