BEIRUT, Lebanon — Syrian rebels said they seized an important military airport and an air defense base just outside Damascus on Sunday, adding to a monthlong string of tactical successes — capturing bases, disrupting supply routes and seizing weaponry — that demonstrate their ability to erode the government’s dominance despite facing withering aerial attacks.

Over the past month, rebels have seized or damaged major military bases around the country, making off with armored vehicles, antiaircraft weapons and other equipment they desperately need to break the stalemate in the grinding conflict, which has taken more than 30,000 lives. But they have not tried to hold all of the bases, as they become easy targets for government airstrikes.

The capture of the air base near Damascus, Marj al-Sultan, could be significant because it was one of the principal bases used by the Syrian Air Force’s fleet of Mi-8 helicopters, said Joseph Holliday, a senior analyst covering Syria for the Institute for the Study of War in Washington. The government relies on the aircraft to resupply army units and to carry out bomb and rocket attacks, especially in the north where government forces are increasingly isolated and air power is the main way to harass the rebels.

Still, despite videos of rebels seizing weapons caches, analysts said the recent successes appeared unlikely to produce a sudden shift in the balance of power, since the government seems to be consolidating its forces to defend core areas.