The role of parliamentary speaker is a powerful position in Iranian politics and analysts said Mr. Larijani could use it to challenge the president, Mahmoud Ahmadinejad, against whom Mr. Larijani ran for president in 2005. Mr. Larijani won the speaker position by a vote of 232 to 31.

Mr. Larijani resigned as chief nuclear negotiator last October. He was among a small group of officials who, while supportive of Iran’s nuclear ambitions, had tried to press back against Mr. Ahmadinejad and his more radical approach, which had left Iran increasingly isolated. After Mr. Larijani’s election as Parliament speaker Wednesday, he used a speech in Parliament to strongly criticize a report published this week by the International Atomic Energy Agency that had raised concerns about what it called Iran’s research into the development of nuclear weapons.

He described the report as “deplorable" and said that in the future Iran might limit its cooperation with the United Nations nuclear agency, The Associated Press reported.

Mr. Larijani, a conservative politician and the former head of state-run television, had been appointed to the nuclear post by Ayatollah Khamenei, Iran’s supreme leader, to whom Mr. Larijani also answered.

His departure suggested that Ayatollah Khamenei had swung behind Mr. Ahmadinejad and his tougher approach on the nuclear issue, in which Iran has defied the United Nations Security Council’s demand that Iran quit enriching uranium. Instead, Iran has accelerated the process of uranium enrichment.

Ahead of the vote for speaker, analysts in Iran had speculated that Mr. Larijani might use the election as a test of his popularity. If successful, he might resign from his post and run for the presidency, they said. They said he was in a stronger position than he was three years ago because of his time as the country’s chief nuclear negotiator for which he won a strong reputation inside Iran.

At the time of his resignation, there was speculation by political Web sites in Iran that Mr. Ahmadinejad and Mr. Larijani had differences over tactics and how to pursue talks with Europe.

Analysts referred to Mr. Ahmadinejad’s confrontational talk and how his speeches about Iran’s nuclear program had complicated Mr. Larijani’s negotiations with European leaders.

In an unusually blunt and detailed report, the International Atomic Energy Agency said Monday that Iran’s suspected research into the development of nuclear weapons remained “a matter of serious concern” and that Iran continued to owe the agency “substantial explanations.”

Iran insists its uranium enrichment program is devoted solely to producing fuel for nuclear reactors that generate electricity. But the United States and some European countries contend that it may be used for a nuclear weapons program.