TEL AVIV — Israel’s new missile and rocket defense system failed to deter Palestinian attacks from the Gaza Strip, a report said.

The Institute for National Security Studies asserted that Israel’s Iron Dome intercepted about 80 percent of missiles and rockets fired from the Gaza Strip earlier this month. The report by Mark Heller said the percentage was not sufficient to deter Palestinian gunners.

“Unless active defense is 100 percent effective, it will not eliminate the need for passive defense or prevent massive disruption of normal life inside the envelope of the rockets,” the report, titled “The Last Round in Gaza — and the Next,” said. “Nor will it spare the government the need to take weighty strategic decisions that it would prefer to avoid.”

It was not clear how the report computed the 80 percent interception rate. Israeli military sources, who at various points asserted interception rates of between 85 and 90 percent, reported that Palestinian gunners fired some 320 missiles and rockets into Israel, with close to 50 interceptions. They said most of the projectiles were not targeted and fell in open areas.

Heller said Iron Dome, with three batteries in southern Israel, underwent its first operational test during the mini-war with the Gaza Strip. He said the system, developed by the state-owned Rafael Advanced Defense Systems, succeeded in identifying rockets that threatened Israeli communities.

“As a result, many Israeli fatalities and injuries were undoubtedly prevented and extensive property damage was avoided,” the report, dated March 18, said. “That result validates the economic rationale of the project, despite the huge cost imbalance between cheap rockets and missiles coming out of Gaza and expensive interceptors sent up to destroy them.” But the report said the 80 percent interception rate fell short of making Iron Dome into what was termed a “strategic game-changer.” The report said the prospect of 20 percent success would spur Palestinian gunners to keep firing missiles and rockets into Israel.

“Palestinian rocket attacks were ended this time — and will perhaps be deterred next time — only by offensive operations that kill or threaten to kill those directly involved and constitute a threat of unacceptable disruption or damage to the lives of their relevant constituents: the Palestinian public,” the report said. “In other words, coercion/deterrence by punishment remains the dominant motif in this discourse.” (Copyright © 2012 East West Services, Inc. 03/20/12)