Even if Iran were to choose this path, American officials said it would probably take Iran some time to reconfigure its nuclear facilities to produce weapons-grade uranium and ramp up work on designing a nuclear warhead.

Israeli officials have indicated that if they saw a race for the bomb under way, they would probably take military action and encourage the United States to join the effort. A spokesman for Israel’s embassy in Washington declined to comment for this article. In interviews, Israeli officials said their assessments were coming into line with the American view, but they remain suspicious that Iran has a secret enrichment site yet to be discovered.

American officials said, in contrast to a year ago, that Iran’s nuclear program was not currently the central focus of discussions between top leaders in Washington and Jerusalem. During the last visit to Washington by Prime Minister Benjamin Netanyahu of Israel in early July, the Iranian program was relatively low on the agenda, according to one senior administration official.

To block Iran’s nuclear ambitions, the United States and the European Union recently imposed harsh economic sanctions aimed at choking off Iran’s energy supplies and prohibiting foreign banks from doing business with financial institutions inside the country.

Several officials said they believed the mounting cost of the economic sanctions, especially those affecting Iran’s ability to import gasoline and develop its oil fields, has created fissures among Iran’s political elite and forced a debate about the costs of developing nuclear weapons.

“The argument is over how far to push the program, how close to a weapon they can get without paying an even higher price,” said the senior administration official, speaking on condition of anonymity because American assessments on these debates are classified. “And we’re beginning to see a lot of divisions inside the leadership on that question.”

Nuclear experts agree that the hardest element of producing a weapon is obtaining weapons-grade material. And for Iran that quest, which stretches back more than 20 years, has not been going well, by most accounts.