But it is unclear how much leverage Israel has to press its anti-Iran agenda diplomatically.

Israel has little stomach for Mr. Assad’s regaining full control of Syria: One senior government official likened it to “swallowing a poisoned frog,” given that Mr. Assad had gassed his own people.

So a willingness to accept Mr. Assad’s resumption of control over all of Syria is no small concession, said Amos Yadlin, a former chief of Israeli military intelligence who now heads the Institute for National Security Studies in Tel Aviv.

“Nobody can these days destabilize the Assad regime,” he said. “The only one who can do it is Israel. And the Russians know that very well. So to get a commitment from Israel not to destabilize Syria is something that Russia will value very much.”

Mr. Assad, while an avowed enemy of Israel, has taken pains to avoid a battle with Israel and has maintained the truce that has held since 1974.

“We haven’t had a problem with the Assad regime,” Mr. Netanyahu said, according to the Israeli newspaper Haaretz. “For 40 years, not a single bullet was fired on the Golan Heights.”

But Israel’s threats — to interfere with Mr. Assad’s efforts to recapture southwestern Syria, or to retaliate against Iranian forces’ entrenchment in Syria with strikes against Iranian and Syrian government positions — are getting old, said Ofer Zalzberg, an analyst at International Crisis Group: “Moscow tolerated it for awhile, but they’re unhappy with this as a long-term pattern,” he said.

Even if it agreed with the Israeli position, there are limits to what Russia can do. Russia could be expected to do little more than “communicating with Iran and asking them politely” to move farther from the Israeli border, and its promises would likely be both short-lived and difficult to enforce, Mr. Zalzberg said. “I don’t see Russia as likely to deploy a sizable contingent of its military police in the southwest with some kind of endless duration,” he said.