POLICE have detained Shanghai activist Zhu Fuming for taking part in the waves of pro-democracy protests that have hit the administration this spring. And security officials in the east China city are trying to track down the identities of the 54 signatories to a petition on political reform that was sent to the National People's Congress (NPC) on Friday. Sources in the dissident community said Zhu, who is in his early 30s, was detained early this month following a spate of run-ins with local security agents. A college graduate and an employee in a company that provides information for citizens seeking to go abroad, Zhu is loosely associated with the Shanghai-based Association for Human Rights. Before his detention, he was hauled in for brief questioning at least twice this year. The first time was after police found Zhu had secretly taped their conversation with him. The second was at a Shanghai disco after Zhu shouted on the dance floor slogans calling for overturning the verdict on the Tiananmen Square crackdown. Zhu's relatives indicated yesterday they had not been told by local police where he was being held or for what reason. Out of fear of the authorities, however, the relatives have not taken any action. Meanwhile, Shanghai sources said police were investigating the ''background'' behind last Friday's 19-point petition, which called for constitutional amendments to introduce a multi-party system. It is understood that while the petition to the NPC stated 54 people had signed it, only seven names appeared on the document. ''Police are trying to find out who the 47 unnamed signatories are,'' a source said. ''They also want to check if an 'anti-government' organisation is behind it.'' The source said the local procuratorate yesterday tried to get into contact with Dai Xuezhong, an activist who spent two years in a re-education through labour camp after the June 4, 1989, crackdown. It is understood that Mr Dai, now a private entrepreneur, yesterday refused to respond when officers tried to contact him through his pager. Dissidents in Shanghai said the authorities were alarmed by the petition because it was more radical than similar ones organised this month by Beijing-based intellectuals such as Xu Liangying, Wang Dan or Liu Nianchun. They said copies of the petition had been sent by mail to intellectuals in the big cities.