THE Government yesterday announced the appointment of the three top policemen to head the force in the run-up to the 1997 change of sovereignty. The new Commissioner of Police will be Eddie Hui Ki-on, 50. His two deputies will be Peter So Lai-yin, 51, and Peter Wong Tsan-kwong, 48. The appointments mean only one expatriate officer - Deputy Commissioner John Thorpe - remains in the top policy ranks of the force. However, he is expected to retire in October as the head of the Special Branch, a wing being rapidly disbanded prior to its re-formation in 1996 under a less clandestine charter. Mr So, who recently took over his new position as deputy commissioner in charge of management, was previously senior assistant commissioner (director of personnel and training). Mr Wong, who will be in charge of operations, was senior assistant commissioner (director of crime). Mr Hui, who takes up his post on July 3, said yesterday he wanted to stay in charge of the 27,000-strong force until the year 2000. He promised that police would be ''at the forefront'' of ''great challenges'' in the territory in the years prior to 1997. He replaces Li Kwan-ha, the first local police commissioner. Mr Li will retire on his 57th birthday after 41/2 years in the top job. He is an intensely private man and even close colleagues do not know what he intends to do after he steps down. Mr Li will be best remembered for initiating improved links with mainland police and security officials. In fact, he was in China yesterday on police duties when Governor Chris Patten announced the appointments.