Mr. Obama argued for a slower course, saying, “We are going to want to make sure that we can continue to move towards less emphasis on nuclear weapons,” and, he added, to “make sure that our conventional weapons capability is an effective deterrent in all but the most extreme circumstances.”

Image President Obama on Monday discussing his new nuclear strategy, which would limit the conditions for using such weapons. Credit... Stephen Crowley/The New York Times

The release of the new strategy, known as the Nuclear Posture Review, opens an intensive nine days of nuclear diplomacy geared toward reducing weapons. Mr. Obama plans to fly to Prague to sign a new arms-control agreement with Russia on Thursday and then next week will host 47 world leaders in Washington for a summit meeting on nuclear security.

The most immediate test of the new strategy is likely to be in dealing with Iran, which has defied the international community by developing a nuclear program that it insists is peaceful but that the United States and its allies say is a precursor to weapons. Asked about the escalating confrontation with Iran, Mr. Obama said he was now convinced that “the current course they’re on would provide them with nuclear weapons capabilities,” though he gave no timeline.

He dodged when asked whether he shared Israel’s view that a “nuclear capable” Iran was as dangerous as one that actually possessed weapons.

“I’m not going to parse that right now,” he said, sitting in his office as children played on the South Lawn of the White House at a daylong Easter egg roll. But he cited the example of North Korea, whose nuclear capabilities were unclear until it conducted a test in 2006, which it followed with a second shortly after Mr. Obama took office.

“I think it’s safe to say that there was a time when North Korea was said to be simply a nuclear-capable state until it kicked out the I.A.E.A. and become a self-professed nuclear state,” he said, referring to the International Atomic Energy Agency. “And so rather than splitting hairs on this, I think that the international community has a strong sense of what it means to pursue civilian nuclear energy for peaceful purposes versus a weaponizing capability.”

Mr. Obama said he wanted a new United Nations sanctions resolution against Iran “that has bite,” but he would not embrace the phrase “crippling sanctions” once used by Secretary of State Hillary Rodham Clinton. And he acknowledged the limitations of United Nations action. “We’re not naïve that any single set of sanctions automatically is going to change Iranian behavior,” he said, adding “there’s no light switch in this process.”