BEIJING (AP) _ China today released ailing dissident Chen Ziming, just weeks before the expected arrival of U.S. Secretary of State Warren Christopher on a visit to improve ties.

Chen, jailed as a ``black hand'' behind pro-democracy protests on Tiananmen Square in 1989, was freed on medical parole and arrived home tonight, saying he was tired, his younger brother Chen Ziping said.

``Chen Ziming's situation has improved,'' the brother said. ``We are very happy.''

Last week, a Chinese court convicted Wang Dan, one of China's last active democracy activists, on subversion charges and sentenced him to 11 years in prison. The United States criticized the verdict.

Chen, who has cancer, was sentenced to 13 years imprisonment for masterminding 1989's Tiananmen Square pro-democracy demonstrations, which the army violently crushed. Chen was convicted of ``counterrevolutionary propaganda and incitement.''

He was freed in 1994 on a medical parole after being diagnosed with cancer, only to be arrested again in 1995 for staging a one-day hunger strike to mark the anniversary of the army's crackdown.

Police said at the time that if he was healthy enough to fast, then he was healthy enough to complete his prison term.

Chen's release come before Christopher visits Beijing later this month to seek improved relations. He is expected to raise human rights, a persistent irritant in U.S.-China ties.

President Clinton raised Chen's case in a meeting in New York last year with Chinese President Jiang Zemin.

Doctors have said Chen needs an operation and should be hospitalized, his sister, Chen Zihua, said.

The family had asked officials all along to release Chen so he can recover either at home or in a hospital.

Chen, 44, was a founder of a think tank, the Beijing Social Economic Studies Institute, in the 1980s. It conducted some of Communist China's first social surveys and produced studies on political and economic reform.

Chen's colleague, Wang Juntao, who also got a 13-year prison term, was released on medical parole in 1994 and allowed to go to the United States for treatment of hepatitis believed contracted in prison.