Iranian and American officials ended a round of high-level nuclear talks here on Monday considering a proposal that would strictly limit, for at least 10 years, Iran ’s ability to produce nuclear material, but gradually ease restrictions on Tehran in the final years of any deal. The proposed phasing out of restrictions is part of a broader effort to mollify critics in Tehran, where some hard-liners in the government and the military oppose any deal that would force Iran to forsake nuclear production for a generation, and Washington, where some members of Congress have objected to an agreement that would not impose lengthy restrictions on Iran’s program. The question of how long any agreement would endure is a critical one: President Obama and Secretary of State John Kerry have said they will not sign an agreement that would give Iran the ability to produce enough fuel for […]