BEIRUT While a tense calm prevailed Saturday in downtown Damascus, the rumbling explosions in the distance, the screech of warplanes overhead and the proliferating security checkpoints in the streets gave the impression that rebels were making their strongest push toward the Syrian capital since the government repelled an offensive there in July, residents and a Western ambassador said.

Syrian rebels and government forces clashed along the Damascus airport road and throughout the capital’s eastern and southern suburbs Saturday for a third day, and there were reports that President Bashar Assad was readying his most loyal and effective divisions to defend the city, the heart of his power.

Military analysts warned that it was impossible to know whether a decisive battle for Damascus was beginning, especially after the government apparently blocked access to the Internet for 53 hours, limiting the flow of information to the outside world. But they said that a government fight to defend its core in the capital could be the fiercest and most destructive phase yet of the 20-month conflict.

“We’re waiting for the big battle to begin,” said Emile Hokayem, an analyst based in Bahrain for the International Institute for Strategic Studies.

For decades, the Assad family has settled loyal military families, many from its minority Alawite sect, in the western suburbs of Damascus, where the presidential palace sits on a plateau overlooking the city. The current fighting suggested that the government was trying to insulate those areas, along with the city center and airport, from the semicircle of urban sprawl in the north and southwest where rebels have strengthened their position in recent days, overrunning a string of small bases.

Analysts say that Assad, knowing that losing Damascus could be a decisive blow, has been conserving his best and most loyal troops and much of his artillery for a battle there.

“We’re not yet at a point where the regime is in total panic mode and can no longer make rational – however nasty – decisions about military strategy,” Hokayem said. “He has to decide which cities around Damascus to destroy and which cities to keep in hand.”

Analysts said rebels were unlikely to quickly overrun the government’s positions in the capital. The government has defended chosen strong points for months, like its most important helicopter base in the northern province of Idlib and a base on the road between Damascus and the commercial hub of Aleppo. Rebels have besieged both for months without taking them.

But the encroachment on Damascus has a profound psychological effect that could hasten the crumbling of Assad’s support – or deepen it among those who fear their fate is tied to his. In July, when rebels briefly held the southern Damascus neighborhood of Midan and bombed a military headquarters downtown, killing four top officials, some government supporters fled to Lebanon and coastal Alawite strongholds, analysts said.

If rebels hit Damascus or assassinate top officials, Holliday said, “you could have more elements of the Alawite leadership saying, ‘I’m not going down with the ship.’ ”