THE murder detection rate in Hongkong lags behind cities such as London and Sydney but still compares favourably with New York, one of the crime capitals of the world, latest figures reveal. Police files in the territory contain 284 cases of murder and manslaughter that remain unsolved over the past 10 years. The number of undetected killings has stayed between a quarter and a third of the total committed in the past decade. Official figures show that police last year were more successful in their hunt for killers, with the detection rate increasing from 66 per cent to 75 per cent, but 27 of the 108 reported cases have still not been cleared up. In London, the Metropolitan Police have kept their detection rate at about the 90 per cent mark, according to a Scotland Yard spokesman. Their most recent figures, for 1991, show that of the 185 killings, 163 were solved - a success rate of 89 per cent. ''Many experts will tell you that the best way to examine how safe an area or city is would be to look at the rate of murder or manslaughter per 100,000 of the population,'' the spokesman said. ''Our figure here in London is 1.2 murders for every 100,000people.'' Criminologist Dr Jon Vagg, of the University of Hongkong, said the comparative figure in the territory was 1.8 killings per 100,000 of the population, which meant that ''we are living in a pretty safe place''. Police in Sydney, Australia's largest city, say they investigated 101 murders or manslaughters in 1991 and solved 92 of them. Sydney's ratio of murders per 100,000 people is 1.7. Dr Vagg said: ''There are unique features to catching criminals in Hongkong. The biggest one is the comparative ease with which murderers can move back over the border and out of the territory. ''This is a problem for police here and I'm sure that with improved co-operation from the mainland, it will cease to be as much of a barrier to investigations.'' Dr Vagg added that because the number of murders in Hongkong was relatively small, any unusual fluctuation could distort figures. ''It can be interesting to look at Hongkong and cities such as London, New York and Sydney. But an example of how easy it is for the figures here to be changed by one event is last year's fire at the Sek Kong detention centre,'' Dr Vagg said. ''The blaze accounted for 23 of the 108 total number of murders, so you sometimes have to look a bit deeper for any trends than just examining the general figures.'' Once city with which Hongkong compares very well is New York. In the five boroughs of New York City there were 1,523 murders reported in the first nine months of last year, said a spokesman for the city's police department. ''That pans out to an average of 169 a month, and the last three months of the year followed the same trend so we expect the year-end total to be about 2,100.'' She admitted that the number of murders per 100,000 people was ''an unfortunately rather high 13.1'' and the detection rate in New York was 57 per cent. ''These figures may seem to be bad on an international scale, but are similar to what other cities have experienced across the States,'' she said. ''Places like Hongkong have stronger legislation on possession of firearms than in the US and consequently weapons are more easily available here,'' she said. One of the 27 remaining local murder cases that have yet to be solved is the brutal killing of American school worker Mrs Ann Boyd, who was found stabbed to death in her Happy Valley flat in December. The officer who last week took charge of the Regional Crime Unit dealing with the investigation said a team of 25 detectives were still involved in the search for the 41-year-old woman's killer. ''This is one of our priority cases and we are determined to catch whoever is responsible for this terrible crime,'' said senior staff officer Mr Trevor Oakes. Dr Vagg added: ''Cases like that of Mrs Boyd grab the media attention, but I would say that you should be more worried about having your car stolen or becoming a victim of credit card fraud than being murdered. ''In fact, there is statistically more chance of you being knocked down by a bus.'' A Royal Hongkong Police spokesman welcomed the news that the detection rate increased last year, saying: ''Hongkong is a comparatively law-abiding place to live.''