SENIOR police ranks are to be localised further by early next year with the expected retirement of another expatriate senior officer. The Deputy Commissioner of Police (management), Mr Keith Lomas, is tipped to step down by the end of 1993 when he reaches 57, the normal retirement age for officers at the level of senior assistant commissioner and above. Although he may serve one more year, like Mr John Sheppard - the retiring deputy commissioner for operations - it is seen as extremely unlikely in the face of localisation before 1997. The director of personnel and training, Senior Assistant Commissioner Peter So Lai-yin, 50, is a strong contender to succeed Mr Lomas. In that event, Police Commissioner Mr Li Kwan-ha's two key deputies would both be local Chinese. Mr Li yesterday announced the promotion of Senior Assistant Commissioner Mr Eddie Hui Ki-on to deputy commissioner following Mr Sheppard's retirement on April 29. Regional commander (Kowloon West), Assistant Commissioner Mr Peter Lee Lam-chuen, will step into Mr Hui's job as director of operations, heading both CID and uniform branch formations. But Mr Lee's portfolio is likely to concentrate on uniform branch operations, because the current review of police structure may result in a new senior assistant commissioner post in charge of CID. Another senior assistant commissioner - instead of the present deputy commissioner - will head the ''sensitive'' Special Branch. The work of the Special Branch is to be scaled down in the run-up to 1997. The branch's anti-espionage work is expected to be scrapped by 1995 at the latest, with serving officers likely to be given the right of abode in Britain. Mr Sheppard's retirement will herald another reshuffle within the top hierarchy of the 26,000-strong force. From April 1, the New Territories police region will be split into two, thus creating an additional post of assistant commissioner. While the current commander, Mr Toby Emmet, is tipped to take over from Mr Lee as head of Kowloon West police, Mr Benny Ng Ching-kwok and Mr Tsang Yam-pui are set to share their responsibilities in running regional police in the New Territories. Mr Ng is currently acting director of management services, as director Mr Jim Main is chairing a police study team looking into a new command structure. Mr Tsang is presently deputy director (crime). At least four chief superintendents are tipped to be promoted to become assistant commissioners in April this year. They are Mr Douglas Lau Yuk-kuen, Mr Tony Ferrige, Mr Ben Munford and Mr John Bagley. Mr Lau, who returned to Hongkong late last year after a one-year course at the Royal College of Defence in Britain, will almost certainly head the crime wing. He headed the Organised Crime and Triad Group before he went on study leave. Mr Ferrige is currently the commandant of the Police Training School. Mr Munford, head of Commercial Crime Bureau, will become director of inspection services. He was one of the department's chief staff officers chairing an inspection team between 1987 and 1989. Mr Bagley, Mr Lee's deputy in the West Kowloon police region, is to take over from Mr Lau To-yee as deputy director (support) following Mr Lau's retirement later this year. Mr Main, when he finishes his review of police structure, may become regional commander of Marine Police with the retirement in December of Mr Barrie Deegan who will reach 55.