BELGIAN officials have asked Governor Chris Patten to reconsider the decision to reject funding for outspoken arts group Zuni Icosahedron to perform at a Brussels festival. They suggested the Hong Kong Government give about $2 million towards the May festival, in which some other Hong Kong projects would be involved, if it refused to support Zuni directly. But Principal Assistant Secretary for Recreation and Culture (Culture), Wan Chung-chu, said the plea would be rejected. Organisers of Brussels' first International Arts Festival wrote last week after the Hong Kong Government said it would not fund Zuni. Zuni had applied twice for $2.8 million to stage a performance but was turned down by a joint meeting comprising members from Council for the Performing Arts, working group on the Arts Development Council, and the Recreation and Culture Branch. It is understood members considered that ''as a majority of Zuni's members were not trained professionals, it seemed improper for them to present professional artists' production in an international arts event on a big scale''.