The deal does not roll back the vast majority of the advances Iran has made in the past five years, which have drastically shortened what nuclear experts call its “dash time” to a bomb — the minimum time it would take to build a weapon if Iran’s supreme leader or military decided to pursue that path.

Lengthening that period, so that the United States and its allies would have time to react, is the ultimate goal of President Obama’s negotiating team. It is also a major source of friction between the White House and two allies, Israel and Saudi Arabia, which have made no secret of their belief that they are being sold down the river…

Mr. Kerry and his chief negotiator, Wendy Sherman, say they have no illusions that the interim agreement solves the Iranian nuclear problem. It simply creates time and space for the real negotiations, they say, where the goal will be to convince Iranian leaders that the only way to get the most crippling sanctions — those that have cut the country’s oil revenue in half — lifted is to dismantle large parts of a program on which they have spent billions of dollars and staked national pride.

“Rollback may be a step too far for the Iranians,” said Vali R. Nasr, the dean of the School of Advanced International Studies at Johns Hopkins University. Iran’s recently elected president, Hassan Rouhani, “can’t go there for some time,” Dr. Nasr said, “because he can’t been seen at home giving up such a huge investment or abandoning national security.”