JUVENILE crime fell by eight per cent last year, sparking hopes of a turnaround in the dramatic upsurge of juvenile arrests which started five years ago. But a clinical psychologist has cautioned that the drop could be because the more serious offenders have become organised, sophisticated and harder to arrest. The number of offenders under 15 doubled from 1988 to 1989, but last year's figures represented a four-year low. Statistics show 6,491 juvenile offenders were arrested last year compared to 7,437 in 1989. Figures were not available for arrests of offenders aged 14 to 21, but the Correctional Services Department's senior clinical psychologist, Mrs Lu Chan Ching-chuen, said her experience with offenders this age suggested they were ''more inclined to commitmore crime''. ''They have become more sophisticated in knowing their way around,'' she said. ''They used to stick to one triad gang and be bound by its rules, but now they don't mind shifting their loyalties to look after themselves. ''They are more organised and sophisticated.'' The number of violent juvenile crime cases - including rape, serious assault, theft, criminal intimidation, blackmail, robbery and arson - dropped by 7.5 per cent to 1,704 last year. However, Mrs Lu said statistics could be misleading because youths who had learned how to avoid arrest could obscure the real level of crime. Social workers are more optimistic and claim rehabilitation work deters repeat offences. Senior social work officer (community services order) Mrs Winnie Kung Tsoi Wai-yin said volunteers working with probationers had proved particularly effective. They provided friendship and tuition for probationers, to help them develop skills and confidence. Police also claim their educational work could be making youths more responsible. Hongkong's unique Junior Police Corp encourages awareness of crime and assisting police in crime detection. It has more than 200,000 members. A corp spokesman said police officers' talks in schools helped. ''At least some of the problem seems to be purely ignorance, based on some of the students' reaction,'' the spokesman said. ''Many seem surprised when they are told of the consequences of crime; some had not stopped to think that a criminal record could affect their employment chances and chances of emigrating later in life.'' Police also credited a new multi-departmental approach which they hope will be endorsed in a formal report by the end of the year. Representatives from the police, education and social welfare departments joined forces on a working group last year to compile a comprehensive report on juvenile crime for the Fight Crime Committee. It is expected to include recommendations for changes to government policy and to police procedure to increase the input of social welfare and education workers. Detective Superintendent Graham Lander, who is in charge of the Crime Prevention Bureau, said the group was looking at ''the whole question of juvenile crime, including repeat offenders and after-care''. An independent crime analyst said the drop in juvenile crime was marginal and could be temporary, especially given that the number of juvenile offenders increased marginally from 1,603 in the last quarter of 1991, to 1,674 in the same period last year. But police said the multi-departmental approach could help sustain the trend. Mrs Lu also welcomed the multi-departmental approach because it could target the root problems of the highest-risk groups. She completed a five-year longitudinal study on recidivism late last year which cited a 1991 Swedish study showing 5.4 per cent of repeat offenders responsible for 26 per cent of offences. The study also showed Hongkong repeat offenders shared common factors including disadvantaged or broken families, family members who were criminals, lack of emotional support from family, involvement with drugs, preference for a hedonistic lifestyle, non-productivity in study or work, and known association with triads or gangs. A multi-departmental approach on such offenders would focus efforts on a group responsible for a disproportionate amount of offences. It would unite scattered information and skills to tackle the roots of the problem, Mrs Lu said.