Moreover, he appeared to impose new conditions, insisting that international sanctions not be lifted as long as Iran continues its aggressive behavior, including hostility toward Israel and support for Hezbollah, which has called for Israel’s destruction.

Mr. Netanyahu has two main objections. One is that an agreement would not force Iran to dismantle its nuclear facilities and would leave it with the ability to enrich uranium and, in time, to produce enough nuclear fuel for a bomb. Two, that a deal to severely restrict Iran’s ability to produce nuclear fuel for a decade or more is not long enough. He also dismisses the potential effectiveness of international inspections to deter Iran from cheating.

While an agreement would not abolish the nuclear program, which Iran says it needs for power generation and medical purposes, neither would walking away. Even repeated bombing of Iran’s nuclear plants would not eliminate its capability because Iran and its scientists have acquired the nuclear know-how over the past six decades to rebuild the program in a couple of years.

The one approach that might constrain Iran is tough negotiations, which the United States and its partners Britain, France, China, Germany and Russia have rightly committed to. If an agreement comes together, it would establish verifiable limits on the nuclear program that do not now exist and ensure that Iran could not quickly produce enough weapons-usable material for a bomb. The major benefit for Iran is that it would gradually be freed of many of the onerous international sanctions that have helped cripple its economy.

While no Iranian facilities are expected to be dismantled, critical installations are expected to be reconfigured so they are less of a threat and the centrifuge machines used to enrich uranium would be reduced. Iran would be barred from enriching uranium above 5 percent, the level needed for power generation and medical uses but not sufficient for producing weapons-grade nuclear fuel. Absent a negotiated agreement, Iran will continue with its program without constraints.