* Israel fears Syria may hand chemical weapons to Hezbollah
* Hezbollah has received support from Syria and Iran
* Israel accuses Hezbollah and Iran of Bulgaria bombing (Adds details)
By Ori Lewis
JERUSALEM, July 20 (Reuters) - Israel said on Friday it would consider military action if needed to ensure Syrian missiles or chemical weapons did not reach President Bashar al-Assad's allies in Lebanon, the Shi'ite Islamist movement Hezbollah.
"I have instructed the military to increase its intelligence preparations and prepare what is needed so that ... (if necessary) ... we will be able to consider carrying out an operation," Defence Minister Ehud Barak said in an interview on Channel 10 television.
"We are following ... the possible transfer of advanced munitions systems, mainly anti-aircraft missiles or heavy
ground-to-ground missiles, but there could also be a possibility of the transfer of chemical means (weapons) from Syria to Lebanon," said Barak.
"The moment (Assad) starts to fall we will conduct intelligence monitoring and will liaise with other agencies."
Hezbollah, which in the past has received military and financial support from Syria and Iran, launched thousands of mainly short-range rockets into Israel during the Jewish state's 2006 offensive in southern Lebanon. Some longer-range rockets reached central Israel.
The Israel-Lebanon border has been largely quiet since then.
Israel has accused Hezbollah and Iran of carrying out a suicide bombing in Bulgaria on Wednesday that killed five Israeli tourists at Burgas airport, a popular gateway to the Black Sea coast. Iran has denied any involvement.
On Thursday, Barak toured the Golan Heights, a strategic plateau that Israel captured from Syria in the Middle East war in 1967 and from where it can monitor movements inside its northern foe.
Syrian rebels assassinated four of Assad's closest aides in Damascus and seized three border crossings with Iraq and Turkey this week, putting the Syrian leader under greater pressure than at any time in the 16-month uprising against his rule. (Writing by Ori Lewis, editing by Tim Pearce and Ralph Gowling)