TEL AVIV, May 31 (Reuters) - Syria is heading for collapse and will become a "warehouse of weapons" for Islamist militants as it descends into chaos, a senior Israeli army commander said.

"Syria is in civil war, which will lead to a failed state, and terrorism will blossom in it," said Major-General Yair Golan, making a rare public appearance at a conference at Bar Ilan University on Wednesday. "Syria has a big arsenal."

The Arab republic's stock of mainly Russian-made weapons includes surface-to-air missiles, surface-to-surface missiles and marine missiles.

It also possesses chemical weapons which Syria never used in its wars against Israel but which could be attractive weapons for militants, the general said.

"The risk to Israel is taking shape," said Golan, who is commander of Israeli forces on the border with Lebanon and the disengagement line with Syria in the Golan Heights.

"The challenge we are facing is a huge one," he added, according to a translation.

The Israel Defence Forces were "deeply engaged in getting ready, with plans and physical means" along the borders, the Northern Command chief said, without offering specific details.

It was very difficult to forecast how Syria would break up, Golan said. It could be effectively "cantonised" by the conflict that has raged for 14 months since President Bashar al-Assad turned his army on protesters and a rebel force fought back.

Golan said Assad's ally Iran was trying hard to help the president stay in power, and Iran's Lebanese ally Hezbollah was in turn a very determined enemy of Israel which has "no intention of letting us off easily".

"HITTING THEM HARD"

Hezbollah "feel obligated to their guardian (Iran) and when needed they are going to do what Iran is interested in", he told an academic audience at the Begin-Sadat Centre for Strategic Studies.

Hezbollah is the most potent hostile military force directly on one of Israel's borders, but it has done nothing evident in the past 14 months to exploit the Syrian crisis or start trouble with Israel to divert attention from Assad's bloody crackdown.

The Shi'ite movement was focused on creating a "comprehensive ballistic array", Golan said. At the moment, most of the estimated 60,000 rockets and missiles Hezbollah has in place are short-range, low-payload rockets.

"It's not nice to live under this threat in northern Israel, but this type of threat is not a decisive factor against Israel," he said. "Let's not exaggerate when we talk about it."

Hezbollah also has longer-range and more accurate missiles and hopes to obtain more to threaten all of Israel, he said.

If Hezbollah were to attack, however, it could expect massive retaliation which would not be limited to Israeli air power, Golan said. Reliance on air power alone was "an hallucination". There would also be a war of "manoeuvre", he said, signifying a land offensive.

"We need a combined effort," Golan told the conference.

In the event of a third Lebanon war, he said, the IDF would aim to "set back the next threat for a long time by hitting them (Hezbollah) very hard so they won't feel like engaging us again for many, many years".

Israel invaded Lebanon in 1982 to dislodge Palestinian militants operating in the country. It finally withdrew its forces in 2000, but went back to war in 2006, clashing with Hezbollah guerrillas. About 1,200 people, mainly civilians, died in Lebanon in the subsequent fighting, along with 158 Israelis, mostly soldiers.