THE bleak housing estates which make up Tuen Mun are renowned as a haven for criminal activity. Gangs of teenagers loiter on stairwells taking drugs and mugging people to get cash to feed their habit. Triad activity is rife and there is an air of desolation about the place. Statistics show that students drop out of school earlier than in other parts of the territory and workers earn less than the average. Sexual assaults are reported with more frequency in the district, and not just during highlighted periods of press coverage. With only seven per cent of the territory's population, Tuen Mun accounted for nearly 14 per cent of all reported rapes in 1992, and 16 per cent of the rapes in 1991. ''There are so many new people here now. It has become quite bad,'' said a young mother who lives in Leung Chun House, the block where young Ip Wing-sze was raped and strangled to death. ''There's no security and everything is dark. I'm scared.'' Incense burns outside many flats and on their doors are messages designed to appease the spirits of the dead. But at Leung Chun House, it seems the spirits of the living are more restless. The door of one of these flats opened slowly as the woman of the house suspiciously eyed visitors. ''I think there is a bad atmosphere around the complex now,'' she said. ''People are frightened.'' She said she no longer left her apartment alone and said many of her friends were equally cautious. ''We need more security,'' she said. ''They need gates at the entrance.'' Long-term complaints about safety in the housing estates prompted government officials to move ahead with plans to upgrade security in Tuen Mun last year. However, the $250 million approved last week will only pay for a small portion of the safety systems advocated. Psychologists and criminologists the world over have recognised that the anonymity and isolation of public housing estates can create breeding grounds for criminals. ''I suppose the standard thing to say is, when you have people living in large anonymous urban environments, there is an absence of traditional control mechanisms, such as family, or relatives,'' said Dr Harold Traver, a lecturer with the Department of Sociology at Hong Kong University. ''This isolation is conducive to delinquent, criminal activity, although that activity does not necessarily have to be violent,'' he added. Tuen Mun, the focus of many sexual attacks in recent years, may suffer from some of the most severe factors. Far removed from the centre of Hong Kong, it is really a separate city, much as the New Towns concept intended. However, in spite of the development of shopping and recreational facilities, Tuen Mun never became a community with the strong social bonds and kinships of traditional towns. One need not look to the statistics for confirmation of the anxiety that prevails in the public housing estates. Young girls hurry home, eyes downcast. And young women tell of lewd looks and comments in the housing lifts.