FORMER world marathon champion Rob de Castella will still compete internationally - but over shorter courses. De Castella, who was the world's top marathon runner in 1983 when he held the world title and the world record time of two hours, eight minutes and 18 seconds, said he has less time to train since being appointed director of the Australian Institute of Sport three years ago. The 36-year-old Australian finished 36th in Barcelona, the first Olympics he was unable to finish among the top 10 in three attempts at the gold medal. He finished 10th in the Moscow Games in 1980 and fifth in the Los Angeles Games in 1984. ''I'll concentrate on the 10,000 metres and cross country now. I don't have the time to log 130 miles a week. I now usually do 80-90 miles,'' he said. De Castella made an official visit to the Hongkong Sports Institute and was impressed with what he saw. He said he expects a successful amalgamation of the Sports Institute and the Sports Development Board later this year. ''Hongkong now is very similar to what Australia used to be six or seven years ago. Since the Australian Institute of Sports amalgamated with the Australian Sports Commission, we have been very successful in the whole aspect of sport and administration,''he said.