Israel's Home Command has been conducting a nationwide civil defense exercise involving all its air-defense systems to prepare for a potentially devastating missile onslaught.

Former intelligence chief Amos Yadlin warned Wednesday that the main targets are likely to be Jerusalem and Tel Aviv.

In a related development, a new study by Bar-Ilan University said a growing number of Israelis are obtaining foreign passports in apparent preparation to flee if it looks like war is imminent.

Reflecting the growing unease, Lt. Gen. Gabi Ashkenazi, who retired as chief of staff of the armed forces in February, told a recent gathering of American Jews at a Beverly Hills gala they should send their sons and daughters to serve in the Israeli military.

Yadlin was the latest of several senior figures in Israel's security establishment who have been at pains to warn compatriots they face an unprecedented threat from tens of thousands of missiles and rockets in the hands of Iran, Syria, Hezbollah in Lebanon and the Palestinian Hamas in Gaza.

The scenario for the five-day exercise, which ends Thursday, involves simulated mass attacks by missiles, some carrying chemical warheads.

All 7.7 million people in Israel were urged to participate Wednesday by rushing to shelters and protected rooms when sirens sounded for emergency drills in cities and towns across the country.

The exercise, dubbed Turning Point 5, is the fifth and largest national emergency drills conducted in the past five years after Israel was taken by surprise in the war of July-August 2006 against Hezbollah.

The Iranian-backed Lebanese group unleashed nearly 4,000 rockets and missiles against northern Israel, hitting the industrial center of Haifa, Israel's third largest city with a population of 265,000.

It was the first time Israeli civilians had come under such a sustained bombardment. It lasted all 34 days of the fighting and drove 300,000 people from northern Israel.

The military says this time around Hezbollah has around 45,000 rockets and missiles, some capable of hitting anywhere in Israel from the north.

Hamas in the south is believed to have up to 5,000 short-range rockets.

Military planners estimate that if war erupts, up to 1,000 missiles a day could be fired by Iran, Syria, Hezbollah and Hamas for up to two months, causing thousands of casualties among the civilian population.

But despite the clear indications of the emerging missile threat in 2006, when Israel had no defenses against such weapons, there has been widespread criticism of successive governments for failing to provide effective defensive systems and prepare for the massive bombardment the army anticipates.

So far only two batteries of the Iron Dome system, designed to counter the short-range rockets, have been deployed. Twenty more are needed for a comprehensive defense.

A second system, David's Sling, designed to intercept medium-range missiles, is still in development. It won't be operational until 2013.

Budget restraints, and the demands of service chiefs focused on offensive weapons platforms, have been blamed for delays in developing these ground-breaking systems.

In another instance, the Haaretz newspaper reported that there aren't enough gas masks for the entire population, saying "at the current distribution rate" about 60 percent of the Israeli population would have masks by 2012.

"There are no masks yet in stock for 40 percent of the population. The Defense Ministry and the Finance Ministry have not yet reached agreement on funding the production of the rest of the masks, at an estimated $408.4 million," Haaretz said.

The right-wing coalition government of Prime Minister Binyamin Netanyahu is coming under increasing criticism amid fears that many Israelis, including key people in industry, business, education and the like, will decide to flee before the anticipated firestorm hits.

Haaretz columnist Gideon Levy wrote that the Bar-Ilan study indicates that 100,000 Israelis have obtained German passports.

"Over the past decade, the trend has strengthened and some 7,000 more Israelis join them every year," he observed.

"To these should be added the thousands of Israelis who hold foreign passports, mostly European countries.

"The excuses are strange and diverse but at the base of them all are unease and anxiety, both personal and national," Levy wrote.

"It reflects a mood, a natural and understandable consequence of the real and imagined fears that have been sown here."