BEIRUT, Lebanon -- As Syrian rebels and government forces clashed on the outskirts of Damascus, explosions rumbled in the distance and warplanes screeched overhead, the rebels appeared to be making their strongest push toward the city since the government repelled an offensive there in July.
A tense calm prevailed downtown, but security checkpoints were proliferating and there were reports that President Bashar al-Assad was readying loyal divisions to defend the city, the capital and heart of his power.
Military analysts warned that it was impossible to know whether a decisive battle for Damascus was beginning, especially as Syrians lost access to the Internet for 53 hours, limiting the flow of information, before it was restored Saturday. But they said that a government fight to defend its core 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 outskirts 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 curving from northeast to southwest, where rebels have strengthened their position in recent days.
Analysts say that Mr. 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," Mr. Hokayem said. "He has to decide which cities around Damascus to destroy and which cities to keep in hand."
When Damascus was threatened in July, the government pulled forces from parts of northern and southern Syria -- allowing rebels to consolidate gains in the north -- and there were reports that something similar was happening now. An activist in Damascus said Saturday that elements of the army's feared Fourth Division, led by Maher al-Assad, the president's brother, were at the Aqraba military airport near the Damascus airport. There were unconfirmed reports that other top divisions and special forces were headed for the city, said Joseph Holliday, an analyst at the Institute for the Study of War, in Washington.
"When the rebels score victories in Damascus, it forces the regime to contract more quickly" in the areas that it contests elsewhere, he said.
To some extent that has already happened, one diplomat said. "There are large areas of Syria that are beyond the control of the regime now," the foreign minister of Jordan, Nasser Judeh, said Saturday in Washington. "The opposition and the rebel forces are making serious advances. Things are moving in a different direction compared to what they were a few weeks ago."
Analysts said rebels were unlikely to quickly overrun the government's positions in the capital. The government has defended chosen strong points, including 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 Mr. Assad's support -- or deepen it among those who fear their fates are tied to his. In July, when rebels briefly held the southern 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.
Last month, rebel bombings in Mezze 86, a neighborhood of Alawite military families near the palace, unsettled government supporters amid suspicions of an inside job. In recent weeks, officials have expressed fear of commuting home to the suburbs, worrying that Sunni Muslim conscript soldiers at checkpoints will turn on them, shifting allegiance to the mostly Sunni uprising, analysts and activists said.
On Saturday, a car bomb exploded in Ish al-Wuroor, an Alawite neighborhood at the north end of the palace plateau, activists said, adding to fears that the Damascus fighting would deepen the conflict's sectarian cast.
If rebels hit Damascus or assassinate top officials, Mr. Holliday said, "you could have more elements of the Alawite leadership saying, 'I'm not going down with the ship.' "
With most foreign airlines canceling flights and the roads contested, residents describe a sense of being trapped.
"I'm stuck in Damascus, but I don't want to leave," said an elderly woman whose home in Kafar Souseh, a southern suburb, is near where fighting has raged.
"I haven't left home for six days now," she said in a telephone interview. "I turn off the lights and follow the traces of light trying to see where shelling is coming from, and during the day I watch the smoke from the window and follow its location."
The Old City of Damascus is known for its tranquil atmosphere, with vine-covered alleys, cafes and worshipers resting on the smooth stones of the Ummayad Mosque courtyard. But even there, explosions in the distance have awakened a sense of foreboding, residents and recent visitors say.
Rebels have made tactical improvements recently, shooting down aircraft with missiles and overrunning air bases ringing Damascus. But they have not always consolidated tactical gains. Their push into Aleppo in the fall resulted in a disastrous government retaliation that alienated some rebel supporters.
Rebel success is counted not just in territory, Mr. Hokayem said, but also in the cost to civilians and whether rebels can provide security and services without provoking heavy attacks.
Mr. Hokayem said rebels around Damascus might avoid the mistakes of Aleppo, where the fighters were mainly civilians from the nearby countryside, who lacked a coordinated military and political strategy.
Better-organized units of army defectors in southern Syria and Jordan have been training to attack Damascus, he said.
"Damascus is an opportunity for the rebels to show that they can get their act together better," he said. "I'm not saying they might not mess it up."
Reporting was contributed by Neil MacFarquhar and Hania Mourtada from Beirut; Thomas Erdbrink from Tehran; Hala Droubi from Dubai, United Arab Emirates; and Elisabeth Bumiller from Washington.
This article originally appeared in The New York Times.