“I am stunned at how fast this is moving, and how fast Assad is falling,” said one senior administration official who helps coordinate U.S. policy toward Syria. This official said the U.S. hopes that Russia — recognizing how quickly Assad’s position is deteriorating — won’t oppose a U.N. resolution this week calling for Assad to step down. 

Tommy Vietor, a spokesman for the National Security Council, summed up the new developments Tuesday with this statement: “Assad’s fall is inevitable.  It’s clear his regime is no longer in full control of the country and only continues to take Syria toward a dangerous end.”

According to the latest U.S. intelligence reports, 300 Syrian army soldiers defected Monday in the Damascus suburb of Jisrine; 50 more defected in the town of Rsatan and dozens in other suburbs of Damascus. The defectors joined the opposition force known as Free Syrian Army, the administration official said, adding that the defections continued Tuesday.

The total number of defectors is now roughly 7,000 to 10,000, the official said — impressive but hardly a match for the 300,000-man Syrian army. In addition to the defectors, there are perhaps 15,000 Syrian soldiers who have fled their units and are taking refuge in Jordan, Turkey or Syrian hideouts.

As the Syrian army rushes to protect the newly embattled centers of Damascus and Aleppo, it is pulling some troops out of opposition hotbeds in central Syria such as Homs, Hama and Idlib — leaving those areas more vulnerable to the insurgents. These aren’t yet “liberated zones,” but government control is spotty and weakening by the day, the official said. Simply put, the Syrian army isn’t large enough to maintain control over all of the country.

 The deteriorating situation in Syria has frightened Iran, which sees Damascus as its only Arab ally. This worry promoted a rush visit to Damascus in mid-January by Gen. Qassem Suleimani, the commander of the Quds Force of Iran’s Revolutionary Guards Corps, according to Vietor. Suleimani is said to have offered money, arms and other assistance to Assad, in a sign of Iran’s support.

“Assad is running out of money to continue financing his crackdown and has turned to Syria’s only ally left, Iran, for help, as evidenced by Suleimani’s recent visit to Damascus,” Vietor said.

But at the same time, Iran has opened secret contacts with the opposition, the official said. The Iranians appear to be hedging their bets, and may even offer the opposition limited money and weapons. Such an effort to back two sides at once would be characteristic of Suleimani, who employed similar tactics in Iraq in his role as chief of Iranian covert action.        

The Arab League is pushing a transition plan for Syria that would transfer power initially to Farouk al-Sharaa, Syria’s vice president, who would designate a transition government and call for elections and a new constitution. This plan was presented at the United Nations this week by Nabil el-Araby, secretary-general of the Arab League, and Hamid bin Jassim, the foreign minister of Qatar.

      U.S. officials have been encouraged by how aggressively Arab leaders have moved to force Assad’s ouster, after the failure of the Arab League observer mission to stem the violence in Syria.

     Russia’s position will be crucial in the success or failure of any diplomatic effort to settle the Syrian conflict short of civil war. U.S. officials argue that because of unified Arab support for a change of regime, Russia will harm its long-term interests in the region if it allows Assad to cling to power. The White House was encouraged Tuesday that Russia had slightly shifted its position from saying it would oppose the Arab League resolution to a milder statement saying that it wouldn’t offer support.