Several American officials said they did not believe that the Israeli government had concluded that it must attack Iran and did not think that such a strike was imminent.

Shaul Mofaz, a former Israeli defense minister who is now a deputy prime minister, warned in a recent interview with the Israeli newspaper Yediot Aharonot that Israel might have no choice but to attack. “If Iran continues with its program for developing nuclear weapons, we will attack,” Mr. Mofaz said in the interview published on June 6, the day after the unpublicized exercise ended. “Attacking Iran, in order to stop its nuclear plans, will be unavoidable.”

But Mr. Mofaz was criticized by other Israeli politicians as seeking to enhance his own standing as questions mount about whether the embattled Israeli prime minister, Ehud Olmert, can hang on to power.

Israeli officials have told their American counterparts that Mr. Mofaz’s statement does not represent official policy. But American officials were also told that Israel had prepared plans for striking nuclear targets in Iran and could carry them out if needed.

Iran has shown signs that it is taking the Israeli warnings seriously, by beefing up its air defenses in recent weeks, including increasing air patrols. In one instance, Iran scrambled F-4 jets to double-check an Iraqi civilian flight from Baghdad to Tehran.

“They are clearly nervous about this and have their air defense on guard,” a Bush administration official said of the Iranians.

Any Israeli attack against Iran’s nuclear facilities would confront a number of challenges. Many American experts say they believe that such an attack could delay but not eliminate Iran’s nuclear program. Much of the program’s infrastructure is buried under earth and concrete and installed in long tunnels or hallways, making precise targeting difficult. There is also concern that not all of the facilities have been detected. To inflict maximum damage, multiple attacks might be necessary, which many analysts say is beyond Israel’s ability at this time.