The administration is also racing to complete, in the next several months, a new radar system in Qatar that would combine with radars already in place in Israel and Turkey to form a broad arc of antimissile coverage, according to military officials. The message to Iran would be that even if it developed a nuclear weapon and mounted it atop its growing fleet of missiles, it could be countered by antimissile systems.

The question of how explicit Mr. Obama’s warnings to Iran should be is still a subject of internal debate, closely tied to election-year politics. Some of Mr. Obama’s advisers have argued that Israel needs a stronger public assurance that he is willing to take military action, well before Iran actually acquired a weapon. But other senior officials have argued that Israel is trying to corner Mr. Obama into a military commitment that he does not yet need to make…

None of the steps being taken by the Obama administration addresses the most immediate goal of the United States and its allies: Slowing Iran’s nuclear development. So inside the American and Israeli intelligence agencies, there is continuing debate about possible successors to “Olympic Games,” the covert cyberoperation, begun in the Bush administration and accelerated under Mr. Obama, that infected Iran’s nuclear centrifuges and, for a while, sent them spinning out of control. An error in the computer code alerted Iran to the attack in 2010, and since then many of the country’s nuclear sites have been modified to defend against such attacks, according to experts familiar with the effort.