Lawmakers from both parties urged President Obamato move toward arming the rebels. “The idea of getting weapons in — if we know the right people to get them — my guess is we will give them to them,” Senator Patrick J. Leahy, Democrat of Vermont, said on NBC’s “Meet the Press.”

The White House declined to say whether it believed Israel was responsible for the Damascus explosions, though other American officials said there was no plausible alternative, given the size and precision of the strikes. Josh Earnest, the deputy press secretary, echoed statements by Mr. Obama last week, saying “the Israelis are justifiably concerned about the threat posed by Hezbollah obtaining these advanced weapon systems.”

The Syrian deputy foreign minister, speaking on CNN, called the strikes “an act of war.” But the decision to blame Israel so publicly presented Mr. Assad with a difficult choice. He could retaliate against Israel and risk conflict with the region’s strongest military — an option analysts called unlikely. Or he could refrain, in which case he risks appearing further weakened and hypocritical to supporters and opponents alike, many of whom are united in their antipathy for Israel.

“Why does the regime attack the rebels with Scuds and warplanes while it takes no action on the Israeli raids?” Basil, 35, who lives near the military research center, in Jamraya, asked as he and his wife swept broken glass from their house on Monday.

Noureddin, 50, a lawyer, lives in the Doumar Project neighborhood, where the blasts knocked kitchen crockery from shelves and drove residents into basements for shelter. Noureddin said the attack would anger members of Mr. Assad’s Alawite sect, who make up the bulk of the military elite and his strongest base of support, already frustrated with their mounting death toll.

“Today, President Bashar al-Assad is in a very hard position with his Alawite community,” he said. In a play on Mr. Assad’s surname, which means lion in Arabic, he added, “Today, Israel kills the Alawite soldiers who are protecting the lion’s den.”

The airstrikes shocked residents of Damascus, a relative bubble of security, literally shaking some out of bed. It was a display of firepower far greater than any seen near the capital in two years of war.