Israel has insisted throughout Syria’s two-and-a-half-year-old civil war that it will not intervene except to protect its border or to prevent the transfer of weapons to Hezbollah. There is a stark divide here over whether Mr. Assad’s continued rule is preferable to a victory by Syrian rebel groups, some of whom are allied with Islamic extremists seen as even bigger threats. There is a growing sense that a continuation of the bloody battles may be the best outcome for now.

But Israelis have largely been disappointed by what they describe as Mr. Obama’s indecision — a sharp contrast from their own military secretly striking weapons convoys in Syria that it suspected were bound for Hezbollah several times this year.

Ehud Yaari, a fellow of the Washington Institute for Near East Policy who is based in Jerusalem, said Israelis were dubious about the diplomacy and “confused at the performance of the president.” There was also a concern that both Syria and Iran might obtain advanced Russian weapons systems as part of the deal after the Russian newspaper Kommersant reported on Wednesday that Russia had agreed to give Iran advanced S-300 antiaircraft missiles and build an additional nuclear reactor at the Bushehr nuclear site.

“They got the distinctive feeling that the president was looking for every possible way to avoid acting on the red line which he himself issued,” said Mr. Yaari, a television analyst here with close ties to Israel’s security and intelligence establishment. If Mr. Obama’s “not willing to have a very modest, limited strike on Syria, a punitive strike,” he added, “when we come to that, would he be contemplating a bigger move on Iran?”

But Jonathan Spyer, a senior research fellow at the Interdisciplinary Center in Herzliya, said it was wrong to “draw a simplistic parallel” between Syria and Iran, which the United States has vowed to prevent from developing a nuclear bomb and which is seen as not only as a threat to Israel but a problem for the world.

“The place of Syria and the place of Iran among U.S. national security priorities are very different,” Mr. Spyer said. “If Iran is No. 1 on the list, and Syria is No. 25, you wouldn’t expect the same amount of attention to No. 25 as you would at No. 1.”

Still, Mr. Spyer said he expected that Mr. Assad would turn the Russian plan into an “epic, mammoth filibuster,” and that Israel would probably be left facing an antagonistic nation to the north still harboring chemical weapons as well as an Iran emboldened by a “sense that the West squirms about making statements and then tries not to fulfill them without looking stupid.”