Was it (in part) Israeli fears that caused the US to change its mind on Syria?

The most remarkable news of this week was without doubt the volte face that the US has made with respect to the uprising in Syria. So far the US stand has always been to refrain from direct intervention. But at the  same time it demanded that president Assad must go and it supplied the rebels with arms, in cooperation with Qatar and Saudi Arabia. Also it was at odds with Russia and China, who both refused a to let Assad down a priori and campaigned for a negotiated settlement. 

This week these differences were solved at once. The American Secretary of State John Kerry payed a visit to Moscow, during which he held lengthy meetings wit both President Vladimir Putin and the Russian Foreign Minister Sergei Lavrov. And Tuesday evening at the of the visit, both Kerry and Lavrov announced that Russia and the US have agreed to work towards convening an international conference to find a political solution to the conflict in Syria.

The conference should be convened at the end of May and must try to convince both the Syrian government and opposition to accept a solution based on the core elements of the final communique issued on 30 June 2012, after the UN-backed Action Group for Syria meeting. This meeting of a year ago called for an immediate cessation of violence and the establishment of a transitional government that could include officials serving under President Bashar al-Assad and members of the opposition. Kerry said that the conclusion e of this meeting, which was never carried out, as yet was ''the important track to end the bloodshed in Syria." And he added that 'it must not be a "piece of paper" but rather "the roadmap" for peace."The alternative is that there is even more violence," he added. "The alternative is that Syria heads closer to an abyss, if not over the abyss and into chaos."
So all at once the US dropped the demand that Assad must leave beforehand (although American offcials said that the US still prefers that he steps down)  and left the military option. Russia at the other hand is no longer so adamant that Assad stay. "We are not concerned by the fate of any individual,'' minister Lavrov said. ''We are concerned by the fate of the Syrian people." .
Apparently the US have realized that continuing this war and pushing for the fall of Assad is not bringing the desired solution. What changed the US-diplomats' mind? Was it the fact that the war - which so far already cost some 70.000 people their lives and has caused millions to flee their homes - does not seem to lead to a conclusion soon? Far that islamist factions in the end would be the winners? That Syria was on its way to become a second Iraq?   

At any rate, Abdel Bary al-Atwan, the editor in chief of the Arabic daily Al-Quds al-Arabi had an answer (I quoted this from Juan Cole's blog):

What is the secret word that caused this big change in the US stand and imposed this sudden retreat and shift from the military options that were put on the table before to diplomatic options to reach a political solution through negotiations between the rival parties that have resorted to weapons and bloody confrontations throughout the past two years?
This secret word is made up of seven letters, Israel, in addition to the fear for Israel’s existence within safe and stable borders, ridding it of the specter of war, removing the biggest danger that faces it, which is chaos, and the fear that Syria might become a base for Al-Qa`ida.

And although I doubt that this was the only reason behind the US decision to back down, Al-Atwan may have a point. Take a look for instance at these recent comments (In Foreign Affairs) on the Syrian situation by the former director of the Israeli secret service Mossad,  Efraim Halevy:

 Israel knows one important thing about the Assads: for the past 40 years, they have managed to preserve some form of calm along the border. Technically, the two countries have always been at war -- Syria has yet to officially recognize Israel -- but Israel has been able to count on the governments of Hafez and Bashar Assad to enforce the Separation of Forces Agreement from 1974, in which both sides agreed to a cease-fire in the Golan Heights, the disputed vantage point along their shared border. Indeed, even when Israeli and Syrian forces were briefly locked in fierce fighting in 1982 during Lebanon’s civil war, the border remained quiet.
Israel does not feel as confident, though, about the parties to the current conflict, and with good reason. On the one hand, there are the rebel forces, some of whom are increasingly under the sway of al Qaeda. On the other, there are the Syrian government’s military forces, which are still under Assad’s command, but are ever more dependent on the Iranian Revolutionary Guard and Hezbollah, which is also Iranian-sponsored. Iran is the only outside state with boots on the ground in Syria, and although it is supporting Assad, it is also pressuring his government to more closely serve Iran’s goals -- including by allowing the passage of advanced arms from Syria into southern Lebanon. The recent visit by Iranian Foreign Minister Ali Salehi to Damascus, during which he announced that Iran would not allow Assad to fall under any circumstances, further underscored the depth of Iran’s involvement in the fighting. It is entirely conceivable, in other words, that a post-Assad regime in Syria would be explicitly pro–al Qaeda or even more openly pro-Iran. Either result would be unacceptable to Israel.