THE way society treats its poor, weak and sick is the real test of civilisation. So when protesters smash the windows of a resource centre for Down's syndrome children and put up slogans threatening the lives of the organisers, they do not just shame themselves, they shame the whole of Hong Kong. The residents of the Tung Tau housing estate have for months fought a bitter and acrimonious battle against plans for the centre and a hostel for the mentally handicapped, mounting demonstrations and muttering darkly about the possibility of a breakdown in law and order. Yesterday, they showed they meant it. As police and social workers cleared up the mess, the people of Tung Tau gave anonymous interviews to TV crews claiming this was just the start. One threatened physical violence unless the resource centre was closed down. The Social Welfare Department has already made concessions to the ''sensitivities'' of those living on this housing estate by moving the entrance to the hostel so they would not have to share a lift lobby with the handicapped. They have also promised to increase the size of a mutual aid centre for those living on the estate. When similar problems arose at Laguna City, where plans for a day centre for the mentally handicapped brought more than 1,000 protesters on to the streets, the issue became a political football as angry home owners warned they could not guard against what they described as the ''spontaneous actions'' of individuals. Last night Dr John Tse Wing-ling, chairman of the Hong Kong Down's Syndrome Association and one of those threatened in graffiti on the centre's doors, called for a concerted campaign to end discrimination. He maintained every effort had been made to accommodate the interests of residents. ''Despite the friendly gestures we made, we are not prepared to compromise the rights to community living and integration of children and adults with Down's syndrome,'' he said. Dr Tse is quite correct when he refers to the rights of these innocent people. They are as entitled as anyone to facilities anywhere in Hong Kong, and as entitled to the protection of the law as well. The Government should redouble its efforts to increase tolerance and understanding on this estate. But the police and judiciary should also ensure that those who threaten public order are brought to court and dealt with severely.