Most Israeli analysts, like most officials and analysts abroad, reject these arguments. They say that Iran has been preparing for an attack for some years and will react robustly, as will its allies, Hezbollah and Hamas. Moreover, they say, an attack will at best delay the Iranian program by a couple of years and lead Tehran to redouble its efforts to build such a weapon.

But Mr. Barak and Mr. Netanyahu believe that those concerns will pale if Iran does get a nuclear weapon. This was a point made in a public forum in Jerusalem this week by Maj. Gen. Amir Eshel, chief of the army’s planning division. Speaking of the former leaders of Libya and Iraq, he said, “Who would have dared deal with Qaddafi or Saddam Hussein if they had a nuclear capability? No way.”

General Eshel added that when a senior Indian officer was visiting recently, he was asked why the Indians had done so little in response to the 2008 attacks in Mumbai. “When the other side has a nuclear capability and is prepared to use it, you think twice,” the officer replied, referring to Pakistan.

Mr. Netanyahu has made no secret of his belief that the current Iranian leadership, which has called for Israel’s destruction and which finances and arms militant groups on Israel’s borders, is the contemporary equivalent of the Nazis who tried to eliminate the Jews.

Both Mr. Netanyahu and Mr. Barak argue that sanctions on Iran’s banking and energy sectors, like the ones getting under way, are vital tools for pressuring the Iranian government internally and keeping it under world opprobrium. But they also suspect that such sanctions will not slow the country’s nuclear program and therefore consider a military option to be vital.

“With all the sanctions, which are unprecedented,” Mr. Barak said on the radio this week, “I don’t think we are very close to a situation in which the Iranian leaders will look each other in the eye and say: ‘There is no choice. We have to stop the nuclear program.’ ”

Mr. Netanyahu has told visitors that he believes the Tehran government to be deeply unpopular, indeed despised, and that a careful attack on its nuclear facilities might even be welcomed by Iranian citizens. They might see it, he has said, as the equivalent of removing the crown jewels from a hated monarch.