AN ATTACK by Tung Tau residents on a Down's syndrome association centre was last night condemned by social workers as ''barbaric''. The residents vandalised the building on their estate, smashing windows and daubing a door with messages threatening to kill the centre's head. The vandalism was the latest in a series of demonstrations by residents in Tung Tau against facilities for mentally handicapped people being opened by the Government on the Kowloon estate. Banners and bills opposing the proposed opening in December of the Down's syndrome facility and parent resource centre were also plastered over a nearby garden area yesterday. Their messages called for the closure of such centres and threatened to ''eradicate the mentally handicapped''. Social workers were last night appalled by the residents' ''barbaric behaviour''. Chairman of the Hong Kong Down's Syndrome Association Dr John Tse Wing-ling said he was outraged. ''To challenge and bully the weak is intolerable. For the past few months we have built a constant dialogue with the representatives of the resident committee,'' he said. ''But of late the representatives have refused to conduct discussion with the association. We are sorry that such open hostility has occurred.'' An official for the Commissioner of Rehabilitation of the Health and Welfare Branch, Raphael Li, was last night shocked by the residents' threats. ''That's criminal,'' he said. ''We have, through a consultation paper, made it our policy that we should provide rehabilitation services within residential areas. ''This is one of the most effective ways to rehabilitate the handicapped, and this policy is publicly endorsed. ''We have been explaining to residents why the centre is necessary, and most of them understood and have changed their minds. ''The Government regrets that a few remain so adamant, but public education takes time. ''We do not expect it to have an instant effect. People do not give up their prejudices overnight.'' Mr Li did not know how much money had been spent, but said another $11 million would be committed to public education over the next two years. Legislator Fred Li Wah-ming, a former social worker, said the authorities should pursue the culprits for this ''absolutely irresponsible'' act. ''It seems to be useless to educate them that these children are not harmful to them. They are very friendly and innocent,'' he said. Dr Tse was doubtful public education was the only solution to the problem. He advocated the enactment of legislation to protect and safeguard the welfare of the Down's syndrome population. ''We need anti-discrimination legislation here. Some things cannot be delayed. They are also residents. They have rights to use the premises,'' he said. ''The discriminatory practices and violence against people with Down's syndrome must be stopped. Such stereotyping, prejudice and discrimination is unwanted. ''Tolerance for the milder forms of discrimination permits the more serious forms. It is the right moment for the public and the Government departments to exert concerted efforts to putting an end to discrimination.''