* Israel fears for fate of modern Syrian missiles -sources
* Syria in "disintegration" -Israeli air force chief
By Dan Williams
TEL AVIV, Jan 29 (Reuters) - Syria's advanced conventional weapons would represent as much of a threat to Israel as its chemical arms should they fall into the hands of Syrian rebel forces or Hezbollah guerrillas, Israeli sources said on Tuesday.
Such concerns suggest that Israel, which has signalled heightened readiness over the last week to react militarily if it thinks Damascus is losing control of its chemical arsenal, could also intervene over Syria's Russian-supplied missiles.
"It's clear that unconventional weaponry is a very grave matter. But when you look at the overall, relevant arsenal, Syria has new, advanced (conventional) weapons of a kind you don't find elsewhere in the Middle East," a source briefed on Israeli defence planning told Reuters on condition of anonymity.
A former Israeli national security adviser, Uzi Arad, said in a radio interview on Monday that Syria - where President Bashar al-Assad is battling a 22-month-old armed uprising - had 1,000 tonnes of chemical agents.
Israeli officials have also voiced concern about Syria's advanced Russian-supplied weapons, including anti-aircraft and anti-ship missiles.
Israel fears that should such weapons fall into the hands of the Iranian-backed Hezbollah in neighbouring Lebanon, this could dent the Jewish state's superiority in any future confrontation.
During a 2006 war with Hezbollah, Israel had complete air dominance during countless bombing runs over southern Lebanon, though it was surprised when one of its ships off the Lebanese coast was hit by a cruise missile, killing four servicemen.
Addressing an international aerospace conference on Tuesday, Israeli air force chief Major-General Amir Eshel described Assad's military arsenal as "huge, part of it state-of-the-art, part of it unconventional".
"Syria is the most salient example of a country in the process of disintegration, where none of us has any idea what will happen the day after," he told a conference at the Fisher Institute for Air & Space Strategic Studies near Tel Aviv.
Israel and NATO countries say Syria has stocks of various chemical warfare agents at four sites. Syria is cagey about whether it has such arms but insists that, if it had, it would keep them secure and use them only to fend off foreign attack.
Syria is widely believed to have built up the arsenal to offset Israel's reputed nuclear weapons, among other reasons. Some Israeli experts fear the logic of mutual deterrence would not hold for sub-national Islamist militant groups involved in the rebellion in Syria.
The United States and other world powers have also warned of the danger posed by Syria's chemical weapons.
In his speech, Eshel did not address mounting speculation that Israel could launch preventive strikes in Syria, though other military brass has said such an option was feasible.
But Eshel said the air force was involved in what he termed "a campaign between wars", working with Israeli intelligence agencies in often covert missions. He did not elaborate other than to blame arch-adversary Iran for the lion's share of weapons supplies to Israel's regional enemies.
Sudan, a conduit for arms to the Palestinian Gaza Strip via Egypt, blamed Israel for an attack last October on a weapons factory in Khartoum. Israel also operates regularly in the skies over Lebanon.
"This campaign is 24/7, 365 days a year," Eshel said. "We are taking action to reduce the immediate threats, to create better conditions in which we will be able to win the wars, when they happen." (Editing by Mark Heinrich)