FOUR years after the opening of the Tuen Mun Hospital, patients are still making the long trek to Kowloon because the hospital cannot meet the demand for surgery. Tuen Mun District Board member Chan Wan-sang yesterday called for more resources to be allocated to the hospital to enable it to open fully. He said he feared the lives of the district's 800,000 people were being put at risk because the hospital was operating at half-capacity due to a shortage of manpower. But Tuen Mun Hospital chief executive Dr Cheng Man-yung denied patients' lives were at risk, although he admitted some were suffering inconvenience. He said some surgery patients were travelling to Princess Margaret Hospital in Kowloon, or using private physicians because the hospital could not cope with the volume of work. Dr Cheng said the problem lay in patients waiting for elective surgery - operations for conditions which are not immediately life-threatening - for which they had to make an appointment. Emergency surgery was given priority and dealt with immediately, he said. But the hospital's six-month waiting list for elective surgery was the longest in the territory. Dr Cheng said the hospital's aim was to cut this time in half, but he said this would probably take between six months and a year. Mr Chan said under its original plan the hospital should have opened fully by the end of 1991 or the beginning of 1992. But it was still at a little over half capacity, with only 974 beds out of the planned 1,606 in use and six out of 12 operating theatres open. Mr Chan said the Hospital Authority should allocate more resources to Tuen Mun to enable it to open fully. Both patients and staff were suffering, he said. ''We do think the medical staff have done their best,'' he said. ''Faced with the enormous number of patients, they have worked very hard. ''But if the patients have to go out from Tuen Mun to other areas, it is a hard way for them to get medical treatment.'' Dr Cheng said the problem was that the hospital was being opened in phases and was still expanding - yet the population was increasing quickly. In 1990, the hospital had 12,000 admissions. The following year this leapt to 29,000, and to 45,000 in 1992. In the first three months of this year, the hospital admitted 27,000 patients Dr Cheng said, adding that accident and emergency department cases were rising at a similar rate. ''The hospital location is very convenient for the district so every year we see more and more people.'' He said the hospital had abandoned its original opening schedule because it was felt it would be far better to open services according to need than to a plan made years ago. He was confident the hospital had enough manpower and resources to maintain its current level of service, but said more money was needed to open extra facilities. ''For the current services we are operating, we have enough resources. But for the opening of more hospital services, we do not.'' The hospital had about 10 major projects in the pipeline, he said, including opening its seventh operating theatre within a few months.