The U.S. and Israel are publicly disagreeing over timing for a potential attack on Iran to prevent it from acquiring nuclear weapons.

“There’s a growing concern — more than a concern — that the Israelis, in order to protect themselves, might launch a strike without approval, warning or even foreknowledge,” Aaron David Miller, a former Mideast peace negotiator in the Clinton administration, said today.

The U.S. and Israel have a “significant analytic difference” over estimates of how close Iran is to shielding its nuclear program from attack, Miller said today. The differing views were underscored by public comments yesterday by senior Israeli and U.S. defense officials.

Israeli Defense Minister Ehud Barak said Israel must consider “an operation” before Iran reaches an “immunity zone,” referring to Iran’s goal of protecting its uranium enrichment and other nuclear operations by moving them to deep underground facilities such as one at Fordo, near the holy city of Qom.

“Today, unlike the past, the world has no doubt that Iran’s nuclear program is steadily nearing readiness and is about to enter an immunity zone,” Barak said in an address to the annual Herzliya Conference at the Interdisciplinary Center academic campus north of Tel Aviv.

U.S. Defense Secretary Leon Panetta declined to comment directly on a report by Washington Post columnist David Ignatius that Panetta believes there is a strong likelihood Israel will strike Iran in April, May or June. Panetta and other U.S. officials have repeatedly warned Israel not to act alone against Iran.

“Israel has indicated that they’re considering this” through public statements, Panetta told reporters traveling with him in Brussels yesterday. “And we have indicated our concerns.”

Israelis think Iran will reach the immunity zone in “half the time the Americans think it will,” Miller said. Even so, Miller said, “to take that difference and talk about a growing rift” between Israel and the U.S. “is by and large an overstatement.”

Panetta stressed today that the U.S. and Israel are in agreement on the need to do what is necessary to prevent Iran from becoming a nuclear power.

“We’ve made very clear that they cannot, they cannot develop a nuclear weapon,” Panetta told troops at Ramstein Air Base in Germany.

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