JERUSALEM: Israeli leaders have discussed with visiting American envoys how to manage a Syrian government collapse, an Israeli official said Monday, as Syria made an unprecedented admission of possessing weapons of mass destruction.    

The reference to the chemical and biological weapons came in a threat to use them in case of a foreign attack. The open admission underlined Israel's concerns about the rapidly deteriorating regime of President Bashar Assad.

Israel and the US are concerned that Syria's stockpile of chemical weapons could fall into the hands of militants should the regime in Damascus crumble.

Israeli Prime Minister Benjamin Netanyahu warned Sunday that his country would ''have to act'' if necessary to safeguard this arsenal from rogue poachers.

Syria is believed to have nerve agents as well as mustard gas, Scud missiles capable of delivering these lethal chemicals and a variety of advanced conventional arms, including anti-tank rockets and late-model portable anti-aircraft missiles.

Asked if Israel and the US had discussed managing a Syrian collapse, the Israeli government official said on Monday, ''You can presume that these sorts of issues came up with American officials when they visited recently in Israel.''

He gave no details and spoke on condition of anonymity because he was not authorized to discuss the contents of confidential discussions with reporters.

US National Security Adviser Tom Donilon and Secretary of State Hillary Rodham Clinton visited Israel about a week ago, and Defense Secretary Leon Panetta is expected in Israel next week.

On Sunday, senior Israeli Defense Ministry official Amos Gilad said the Assad government remains in control of its chemical arsenals at this point. Over the weekend, Israeli officials made it clear that Israel was readying options if that changes.

Defense Minister Ehud Barak told Israel's Channel 2 TV that he ordered the military ''to prepare for a situation where we would have to weigh the possibility of carrying out an attack.''

On Sunday, Netanyahu told Fox News that preventing Syria's weapons from reaching Iranian-backed Hezbollah militants in Lebanon was ''something we'll have to act to stop if the need arises.''

''Could you imagine Hezbollah, the people who are conducting with Iran all these terror attacks around the world _ could you imagine them having chemical weapons? It would be like al-Qaida having chemical weapons,'' he said.

Asked whether Israel was prepared to act alone, Netanyahu said Syria's stockpile was a ''common concern'' and that ''we'd have to see if there was a common action to address that concern.''

Israel blames Hezbollah for a number of attacks plotted against Israeli and Jewish targets around the world in the past two years. Israel and Hezbollah fought to a standoff in a monthlong war in 2006.