| HERZLIYA, Israel
HERZLIYA, Israel Israel is poised for a large-scale assault on Syria to prevent advanced weapons reaching jihadi rebels or Hezbollah guerrillas in Lebanon if President Bashar al-Assad is toppled, Israel's air force chief said on Wednesday.
But Major-General Amir Eshel, addressing a security conference, said his warplanes could be repelled by Syria's formidable, Russian-supplied anti-aircraft systems - an implicit censure of Moscow echoed by Israel's defence minister.
"If Syria collapses tomorrow we could find ourselves very quickly inside this cauldron, and on a very large scale, because this enormous arsenal is parked there, just waiting to be looted, and could be turned (against Israel)," he told the Fisher Institute for Air & Space Studies near Tel Aviv.
"We may find ourselves having to take action, on a very broad scale, within a very short period of time," Eshel said. "It does not mean we will act, but that we have to be ready to."
He assumed fighting could escalate to include attacks on Israel by Hezbollah and by Iran, which backs Assad as well as the Lebanese militia, and that the air force may have to employ "the full spectrum of its might".
Israeli warplanes have struck Syria at least three times this year to destroy what intelligence sources described as advanced anti-aircraft and ground-to-ground missile caches in transit to Hezbollah. The Israelis also worry that Assad may eventually lose control of Syria's chemical warheads stocks.
Beset by the more than two-year insurgency that Hezbollah been helping his army battle, Assad has not retaliated to Israel's air strikes. But there are signs his restraint may wane, such as a shooting attack by Syrian troops at an Israeli patrol in the occupied Golan Heights on Tuesday.
While militarily superior to Syria, a foe with which it had been in a stable standoff for decades, Israel fears this edge will be blunted by Assad's Russian-made air and coast defences - especially if Israeli forces are stretched over three fronts.
Eshel said the most formidable of the Russian anti-aircraft systems available, the S-300, was "on its way" to Syria, without elaborating on where he was getting his information.
That suggested that appeals by Israeli Prime Minister Benjamin Netanyahu on Russia to scrap the deal had been unsuccessful.
"Air superiority is critical, and we must contend with a new generation of (Syrian) capabilities," Eshel said.
In separate remarks about Syria to the conference, Israeli Defence Minister Moshe Yaalon said: "There are those who are trying to bring weapons systems into the area that are liable to harm our aerial and naval supremacy ... and this must be prevented in a responsible and considered manner."
Yaalon said that despite recent gains against the Syrian rebels by Assad and Hezbollah forces, Damascus was in decline.
"Assad is losing Syria," he said. "There is a sense that he is charging ahead because of the Russian support, but that story is not over - it could end suddenly, or continue for years as a bloody civil war."
Yaalon played down the prospect of anyone on the Syrian side starting a war with Israel "because they understand the heavy price they would pay".
But neither should Israelis anticipate an easy victory, Eshel told Reuters on the sidelines of the conference.
"People are looking for a knock-out, for things to be surgical and sterile, but they won't be. The homefront will be hit, no matter how much we defend it," he said, referring to possible missile attacks on the Israeli interior from Syria, Hezbollah and Iran. (Writing by Dan Williams; Editing by Jeffrey Heller and Michael Roddy)