WASHINGTON – Iranian democracy activists warned yesterday that one of Iran’s most famous dissidents, Akbar Ganji, who was freed over the weekend, would soon be back in jail if he kept up his criticism of the Tehran mullahs’ regime.

“He has a temporary release,” the editor of American-backed Radio Farda, Ali Sajjadi, said. “And the length of that temporary release is based on what he will do. Probably they won’t take him back to jail if he keeps quiet. Otherwise, if he starts to criticize or to be active again, they will.”

“But I don’t think he can keep quiet,” Mr. Sajjadi added.

Mr. Ganji was serving a six-year term at Tehran’s Evin Prison after his arrest in 2001, when he was detained for publishing “The Red Eminence,” a book in which the dissident linked Iranian political leaders to the murders of prominent critics of the regime in the 1990s.

According to press accounts, Mr. Ganji was granted a temporary release Friday, weighing 108 pounds after months on a hunger strike. Iranian officials were quoted as saying that the dissident had been granted a week-long “leave” in order to celebrate the Iranian New Year, which begins tonight, and that his sentence ends March 30.

An Iranian-born physician, human rights activist, and observer of Mr. Ganji, Ramin Ahmadi, said yesterday that he expected the journalist and his associates to be “cautious” in coming days in order to avoid Mr. Ganji’s being returned to jail.

“I think everyone, from the secularists to the reformists to the radicals, are going to try to be very moderate in their support for Ganji because nobody wants Ganji back in prison,” Dr. Ahmadi said, adding that he expected the dissident to keep a low profile as he tries to “reconnect himself to the outside world.”

In the long term, however, Dr. Ahmadi said he expected that Mr. Ganji “will find a way to create a margin of safety and security around him in order to speak out again,” adding that the journalist was a “genius” at doing so.

Both Dr. Ahmadi and Mr. Sajjadi stressed that Mr. Ganji’s freedom was crucial to the Iranian opposition, saying the journalist would likely lead any organized democracy movement in Iran.

In part because of his summer hunger strike that drew support from the press and world leaders, including President Bush, Mr. Ganji emerged as the most credible voice of opposition inside Iran, they said. His belief that Iran should be secular, and his articulated non-violent strategy for bringing about reform, too, made Mr. Ganji a “figure to keep an eye on,” Mr. Sajjadi said.

Meanwhile, a former student representative to former President Khatemi’s Reform Party, Ali Afshari, said yesterday through an interpreter that the Ganji release was a “setback” and sign of weakness for the regime, which he described as “very vulnerable” in the face of surging domestic discontent.

Yet, he stressed, “At any time, at any moment, if the regime feels he has to go back to prison, they will use any excuse to send him back to jail.”