GENEVA — On the eve of a new round of talks between world powers and Iran, a senior Obama administration official said Wednesday that the United States was prepared to offer Iran limited relief from economic sanctions if Tehran agreed to halt its nuclear program temporarily and reversed part of it. The official said that the suspension of Iran’s nuclear efforts, perhaps for six months, would give negotiators time to pursue a comprehensive and far more challenging agreement. “Put simply, what we’re looking for now is a first phase, a first step, an initial understanding that stops Iran’s nuclear program from moving forward for the first time in decades and that potentially rolls part of it back,” the official told reporters. The long-stymied talks with Iran were re-energized after Hassan Rouhani, the new Iranian president, took office in August and declared that he wanted to resolve longstanding concerns about […]