BEIRUT — Syria’s president promised a national dialogue Monday to consider political reforms, but his vague overtures to a pro-democracy uprising fell flat as protesters took to the streets shouting “Liar!” and demanding his ouster.

In only his third public appearance since the revolt erupted in March, Bashar Assad returned to a now-familiar refrain: He blamed the unrest on “saboteurs,” offered modest potential reforms, but gave no sign he’d move toward ending the Assad family’s political domination.

He clearly intends to try to ride out the wave of protests, showing the steely determination that has kept the Assads in power for 40 years. But the mobilized opposition appeared to be digging in as well, bracing for a showdown in one of the deadliest uprisings of the Arab Spring.

“We want only one thing: Toppling the regime!” read one banner carried by marchers in several cities Monday.

“The timeline is not in (Assad’s) favor,” Mideast scholar Shadi Hamid, at The Brookings Doha Center in Qatar, said after what he called a “disappointing” speech. “The question is, how long can Assad sustain the current situation?”

Standing before a hand-picked crowd of supporters at Damascus University, Assad presented himself as a secure – and beloved – leader intent on protecting his people. He likened some of the country’s troubles to a “germ” that must be fought off.

He said a national dialogue would start soon and he was forming a committee to study constitutional amendments, including one that would open the way to forming political parties other than the ruling Baath Party. He acknowledged demands for reform were legitimate but rehashed allegations that “saboteurs” were exploiting the movement.

A package of reforms was expected by September or the end of the year, he said.

But along with his promises came a warning that his downfall could usher in chaos.

“We want the people to back to reforms but we must isolate true reformers from saboteurs,” Assad said.

He said the country’s economy might collapse unless the unrest ends, calling that “the most dangerous thing we face in the coming period,” a message aimed at his supporters in the business community.

Other dictators across the Middle East — notably Egypt’s Hosni Mubarak — used the same argument as they sought to cling to power during the Arab Spring, warning of chaos in their wake. In Syria, the warning has a special resonance, given the country’s volatile mix of ethnic groups and religious minorities.

The opposition estimates that more than 1,400 Syrians have been killed and 10,000 detained as Assad unleashed his military and security forces to crush the protest movement that erupted in March, inspired by the revolutions in Tunisia and Egypt, and that spread.

Assad, 45, who inherited power in 2000 after the death of his father, President Hafez Assad, previously made a series of overtures to try to ease the growing outrage, lifting the decades-old emergency laws that give the regime a free hand to arrest people without charge, and granting Syrian nationality to thousands of Kurds, a long-ostracized minority. But the concessions did nothing to sap the movement’s momentum.