TEHRAN, SEPT. 28 -- Mehdi Hashemi, who played a key role in exposing the secret U.S. arms sale to Iran, was executed here today, the official Iranian news agency IRNA announced.

Hashemi, a son-in-law of Hussein Ali Montazeri, the clergyman hand-picked by spiritual leader Ayatollah Ruhollah Khomeini to be his successor, was convicted last month of murder, kidnaping and activities against the country, IRNA said. He also had been charged with having links with Savak, the secret service of the deposed shah of Iran, the agency said.

Hashemi was arrested in November after news of a secret trip to Tehran by former U.S. national security adviser Robert S. McFarlane was leaked. Hashemi was widely believed to have played the key role in exposing the affair.

Hashemi had the reputation of being a radical revolutionary bent on forcibly exporting Iran's brand of Islam to neighboring Persian Gulf countries.

Unconfirmed reports said Hashemi had the Tehran hotel where McFarlane was secretly staying under surveillance and that he leaked news of the visit to the pro-Syrian Lebanese publication Ash-Shiraa.

IRNA identified Hashemi only as the former head of the Liberation Movements Bureau in the Revolutionary Guards. It did not mention his position as the director of his father-in-law's office.

Hashemi's execution appeared further to undermine the position of Montazeri, whose nomination is widely reported facing opposition from politicians and clergymen.

Paris-based Iranian opposition sources recently said he had been quietly shelved in favor of a collective post-Khomeini leadership in which Montazeri would be delegated to a secondary role.

Persistent reports over the past few months have suggested that Montazeri was involved in a growing power struggle over Khomeini's succession with other leading figures, including President Ali Khamenei, Parliamentary Speaker Ali Akbar Hashemi Rafsanjani and Ahmed Khomeini, the leader's son.

In Baghdad, the Iraq-based Iranian opposition group People's Mujaheddin said that Hashemi had been executed secretly 10 days ago and that announcement of the execution was withheld until today.