Key leaders of the U.S. Congress want U.S. President Barack Obama to provide funds to help Israel, should it request it, to produce more batteries of the Iron Dome counter-rocket system.

Israel's air force has three batteries deployed to protect cities in the southern Negev Desert against rockets fired by Palestinian militants in the Hamas-ruled Gaza Strip but budget problems mean it can't fund more batteries needed to shield the rest of the country.

Iron Dome, which racked up a 90 percent kill rate against Palestinian Qassam and Grad rockets in recent weeks, was developed by Rafael Advanced Defense Systems and built with the help of a one-time $205 million U.S. grant in fiscal 2011.

The Iron Dome Support Act was introduced Wednesday by U.S. Rep. Howard Berman, D-Calif., ranking member of the House Foreign Affairs Committee, and co-sponsored by Foreign Affairs Committee Chairwoman Ileana Ros-Lehtinen, R-Fla.

The legislation would permit Obama to authorize further funds for the "procurement, maintenance and sustainment" of the Iron Dome system as requested by the Israeli government of Prime Minister Binyamin Netanyahu.

Reps. Gary Ackerman, D-N.Y., the ranking member of the Middle East and South Asia subcommittee; Steve Chabot, R-Ohio, chairman of that subcommittee; David Cicilline, D-R.I.; Ann Marie Buerkle, R-N.Y., signed on as co-sponsors.

Berman observed in a statement that during the latest Palestinian barrage earlier this month Iron Dome "saved innocent lives and prevented an escalation of hostilities and a full-blown crisis.

"Israel must have the ability to defend itself from rocket and missile attacks and the United States will continue to stand by our strong ally if called upon in times of need," he said.

Israeli Defense Minister Ehud Barak says a fourth Iron Dome battery will be deployed within the next few weeks in the south, where 1 million Israelis live within reach of extended-range rockets fired from Gaza.

However, military commanders say they'll need up to 20 batteries to afford effective protection across Israel, not just from short-range rockets fired from Gaza, but larger numbers, possibly 200 a day, from Hezbollah in Lebanon, Israel's northern neighbor.

Some Israeli politicians say Iron Dome is under-funded. Former Brig. Gen. Meir Elran of the Institute for National Security Studies says the offense-oriented air force is reluctant to cut spending on attack squadrons to buy missile-defense systems.

Iron Dome has the capability of assessing which incoming rockets and missiles will hit populated areas, and concentrates on them. Rockets that will land in open spaces aren't engaged.

The Palestinians have fired rockets in relatively small salvos, which Iron Dome clearly can counter to a large extent. But Israeli commanders say that if broadsides are fired in large numbers, Iron Dome won't be anywhere near as effective as it's been so far.

Hezbollah alone has, by Israeli count, more than 43,000 missiles and rockets, with large numbers capable of hitting anywhere in Israel.

This danger cannot be countered by Iron Dome, designed to intercept rockets with a maximum range of 43 miles.

So other systems are needed for the four-tier shield Israel plans, including combating longer range missiles such as Iran's Shehab-3b and Sejjil-2 ballistic weapons.

Rafael is developing a system named David's Sling to counter medium-range missiles.

Arrow-2, currently operational, and the developing Arrow-3 systems built by state-owned Israel Aerospace Industries, working with the Boeing Co., will take care of Iranian and Syrian ballistic weapons.

The United States has been the main funder of Arrow, first deployed in 2000 but remains untested in combat. So far costs exceed $1 billion.

Given Israel's military budgetary restrictions, the government likely will be looking increasingly toward the United States for help in financing David's Sling and Arrow-2 and with Obama facing re-election, he may have little choice but to provide Israel with hefty funding.

Arrow in particular is extremely expensive to operate. Arrow-2 has a shoot-down rate of around 90 percent in trials. But each interception costs $1 million-$2 million, compared to $25,000-$80,000 for Iron Dome.

Military planners fear Israel faces a sustained rocket and missile bombardment, possibly lasting several weeks, by Iran, Syria, Hezbollah and the Palestinians.

The cost of countering this unprecedented attack focused on the civilian population would be immense. U.S. funds would be essential.