A mainland Internet essayist arrested last year after calling for greater democracy in Hong Kong was convicted of subversion but released with a suspended sentence Friday in an unexpected gesture of leniency by the Chinese government.

In a separate case, relatives and overseas human rights groups expressed alarm on Friday about the unexplained detention of an elderly military surgeon who exposed the government's initial coverup of the SARS epidemic last year.

The release of the Internet essayist, Du Daobin, was reported by the official New China News Agency. About 2,000 people across the country, including prominent lawyers, scholars and writers, had signed a petition on the Internet on his behalf and had called on the ruling Chinese Communist Party to stop using the nation's subversion laws to punish people who criticize the government.

Police have repeatedly shut down the Web site hosting the petition, which cited international human rights declarations.

Du, 40, was convicted of "overtly instigating and subverting the state power by way of slander" in connection with 26 articles he posted on the Internet between May 2002 and October 2003, when he was detained, the news agency said. A court in the city of Xiaogan in China's central Hubei province, where Du lives, handed down a suspended three-year prison term and placed him on a form of probation for four years.

Other Chinese dissidents convicted of subversion in recent years have received prison terms of as long as 10 years. The news agency said the court was lenient because Du "was quite cooperative during interrogation."

Reached by telephone, Du's attorney, Mo Shaopin, said Du would be barred from publishing essays during his probation and for an additional two years. He said Du had 10 days to appeal the verdict and sentence.

Wu Wei, a college lecturer who manages one of the Internet sites on which Du posted his essays and who helped organize the petition demanding his release, said the ruling was a victory for Chinese citizens trying to protect their legal rights and demonstrated that the government was "considering the influence of public opinion."

But he said it also showed that the government "still considers speech a crime." As long as the government keeps vaguely worded subversion laws on the books, he said, "the right to free speech of Chinese citizens cannot be guaranteed, and cases like Du's will continue to occur at any time." At least 54 people are in Chinese prisons on charges related to their use of the Internet for political or religious activities.

In the separate case, relatives and human rights groups urged the Chinese government to release Jiang Yanyong, 72, the doctor who helped expose the SARS coverup and who recently called on the party to admit it erred in ordering the 1989 Tiananmen Square massacre.

Jiang and his wife were detained June 1 during a police roundup of dissidents before the anniversary of the June 4, 1989, crackdown on pro-democracy demonstrations in the square. Many of the detained individuals have been released in the past few days, but Jiang and his wife remain in custody.

Jiang's daughter, Jiang Rui, who lives in the United States, said by e-mail that she feared police were preparing to charge him with subversion and had timed his arrest during the annual June roundup to disguise their plan and prevent a public outcry.

She said authorities had asked her brother to deliver her father's dentures and his razor, a sign that he might not be released soon. She said authorities also passed him a note from their mother indicating that the couple would not be able to visit her in California this summer as they had planned.

The U.S.-based group Human Rights Watch urged China to release the doctor and his wife immediately. "China wants to project an image of progress and rule of law," Sam Zarifi, deputy director of the group's Asia division, said in a statement. "But Dr. Jiang's arbitrary detention shows that this government is not bound by constraints."