Washington is not engaged.
While there has been speculation of talks between the two presidents or between US Secretary of State John Kerry and Iranian Foreign Minister Jawad Zarif during the UN meetings, current and former US officials said lower-level contact might make more sense.
"That's often the way they start because you're not really sure what you're dealing with," said a third US official. "You can survive a lower-level meeting that doesn't work, but you can't survive a higher-level that doesn't work."
The United States has several potential candidates to lead the talks, including Wendy Sherman, undersecretary of state for political affairs, who currently leads US nuclear negotiations with Iran, and Bill Burns, deputy secretary of state, who is a past negotiator with Iran and a Middle East expert.
"The level and the negotiator will not be difficult to arrange ... the formal trappings, they'll figure out," said Dennis Ross, a former senior White House official under Obama now at the Washington Institute for Near East Policy think tank.
"If the decision has been made to do it, you cut through that. If they are still fencing around trying to determine how to do it, then that is an indication that there isn't quite the readiness there otherwise would appear to negotiate," he added.
Karim Sadjadpour, an Iran expert at the Carnegie Endowment for International Peace, said a genuine rapprochement between Iran and the United States was unlikely but that an Barack Obama-Hassan Rowhani handshake "could open a path toward detente."
"As long as Ayatollah Khamenei remains supreme leader of Iran, this is the best group of interlocutors that the US will ever have to work with in Tehran, particularly Foreign Minister Zarif," Sadjadpour said.
He argued that Hassan Rowhani and his foreign minister might succeed in impressing other Western nations with their more conciliatory tone and that could, over time, make it harder for the United States to sustain economic sanctions on Iran.
"I think the double-edged sword Hassan Rowhani and Jawad Zarif present to the United States and Israel is that Iran is now easier to engage, but more difficult to isolate," he added.