WELFARE officers working at Tung Tau Estate have been warned about possible trouble after reports that radical elements had taken over a campaign by residents against plans to build a hostel for the severely mentally handicapped at the estate. Mr Anthony Chan Wai-kwan, Assistant Director of Social Welfare, issued the warning even though, he said, the dispute seemed to have eased. The district welfare officer for Wong Tai Sin, Mrs Mable Harvey, said yesterday the situation was ''quite quiet'' and the hostel was being fitted out. ''I spoke to the contractors, who happily report being able to work uninterrupted on the project for the first time,'' she said. ''Providing nothing else happens, we hope the hostel will be able to open sometime between August and October.'' The biggest worry was the recruitment of both staff and residents for the hostel. The ''high profile'' of Tung Tau and its problems could scare people away, she said.