BEIJING has released Lanzhou-based underground Catholic Bishop Yang Libo in another bid to appease its human rights critics. Hongkong human rights lobbyist Mr John Kamm said yesterday he had been informed by the Information Office of the Chinese State Council of Bishop Yang's release from a ''re-education camp'' in Gansu in December. Bishop Yang, 76, had served his three-year jail term, imposed for allegedly organising a clandestine underground bishop conference in Shaanxi in late 1989. However, Mr Kamm and other human rights researchers said there was fear his jail term might be extended because of his ''uncompromising attitude''. ''Other prelates who were imprisoned for taking part in the bishops conference had been released by May last year,'' Mr Kamm said yesterday in San Francisco. ''Bishop Yang's warders reportedly offered to free him. The bishop, however, said he would come out [of the camp] only if the authorities would abolish the [Beijing-organised] Catholic Patriotic Association in Lanzhou.'' Mr Kamm said he began lobbying for the release of Bishop Yang and 11 other elderly prelates in October 1991. On a visit to a prison in Meizhou, Guangdong Province, at that time, he accidentally discovered that the Justice Ministry had an internal regulation which made provisions for the early release of prisoners over 70 years of age. Bishop Yang was the last of the 12 elderly clerics to have been let out of prison. However, one of them, Bishop Chen Jianzhang of Hebei, who is very ill, is feared to be in some form of modified detention. Mr Kamm said there were an estimated 17 Catholic priests and clerics in jail and labour camps, and 22 in ''re-education camps''. A Hongkong-based researcher of the underground church in China said there were 20 to 30 Catholic prelates still in custody. Religious sources in Hongkong said they had not been able to make contact with Bishop Yang since his reported release. ''The diocese of Lanzhou, capital of Gansu, has about 65,000 worshippers,'' a source said. ''It is very short of religious workers, and the priest working there, Father Wang, had been seconded from neighbouring Ping Liang district.'' As in other areas of China, many worshippers and clerics who are active in the ''patriotic'' Catholic establishment in Gansu actually owe their allegiance to the Vatican. Bishop Yang, who was ordained in the underground church in the early 1980s, has the reputation of a fiery anti-communist polemicist. He has reportedly written articles attacking the party's religious policy as well as the ''patriotic'' churches sponsored by the Communist Party. Other religious sources said the release of individual clerics notwithstanding, there were indications the security apparatus had tightened control over the ''illegal'' religious movement. For example, arrests of many affiliates of underground churches had recently been reported in different provinces. Meanwhile, Mr Kamm said the State Council Information Office had denied that former Beijing University student activist Wang Dan had been freed. He said Wang would probably remain in jail until August, when his prison term was up.