Hard-liners in and out of the parliament in Iran have vowed in recent days that those steps would never happen. But Iran’s political establishment seems determined to resolve the nuclear issue as long as there are “positive signs” from the West, insiders close to Mr. Rouhani’s government say.

Iran’s goal is to get the West to accept what its officials say are facts on the ground, and agree that Iran can go on enriching uranium. Since 2002, when an exile group exposed the existence of the program, Iran has managed, despite sanctions and pressures, to expand its fleet of enrichment centrifuges from a dozen to nearly 17,000. And its stockpile of uranium enriched to the lower level could be used to power Iran’s sole semioperating nuclear reactor for several years to come.

“Iran will be a winner when we continue with our peaceful nuclear plans,” Mr. Araghchi said. “The other side will be a winner when they are sure Iran is not after any military or nuclear weapons plans.”

Analysts say that Iran needs, in turn, to be sure of the West’s good faith.

“Clearly, everything stands and falls with this,” said Mohammad Ali Shabani, a Tehran-based analyst who is well informed on the talks. “Iran is ready to take important steps, but for them to accept those, they will need to see some sort of endgame in which they will be sure their rights are accepted.”

By an endgame, Iran means that it wants a timetable of specific steps that Iran would take to make its nuclear activities more transparent, which would ultimately lead to the West accepting that Iran has an independent civilian nuclear energy program, and the lifting of sanctions.

“We now have a new negotiating team in place, which means business and has the full authority to come to an agreement,” said Hamidreza Taraghi, a conservative analyst who has the official task of interpreting the speeches and views of the country’s supreme leader, Ayatollah Ali Khamenei. “We will continue to enrich, but we can talk about the level of enrichment; we will continue to have our stockpile, but can discuss the size of that stockpile.”

The fact that Secretary of State John Kerry will most probably not be present at the talks in Geneva on Tuesday has disappointed some in Iran, especially after the Iranians agreed during the United Nations General Assembly meeting in New York in September to engage in direct talks with the United States, the country that has been the leader in imposing sanctions on Iran.