HONG KONG'S police force was yesterday given a series of assurances about its future by senior Chinese official Lu Ping. He pledged that, after 1997, there would be: No retaliation against officers; No change in conditions of service, and; No interference from the People's Liberation Army. Mr Lu, the Director of Hong Kong and Macau Affairs Office, told visiting Commissioner of Police Eddie Hui Ki-on that he wanted to see the 27,000-strong force continue serving the territory beyond the changeover. Speaking before a half-hour meeting with Mr Lu, Mr Hui said he was confident most officers would stay. ''[Although] in the past they used to serve the Hong Kong British Government, they can still work for the Special Administrative Region government after 1997. Their job of serving the Hong Kong people is the same.'' However, Mr Lu said whether Mr Hui himself could stay in the service beyond 1997 - a wish he has openly expressed - should be decided b y the SAR chief executive. Mr Hui, 50, is tipped to be the first police commissioner of the post-1997 government. He is a non-foreign passport holder and hence is eligible for senior government posts as stipulated in the Basic Law. Mr Lu said Hong Kong's stability hinged on the police's ability to maintain social order, and close co-operation between the police and China's Public Security Bureau was needed. People's Liberation Army units stationed in Hong Kong after 1997 would be limited to a defence role. Police would remain responsible for internal security. The army would obey Chinese and Hong Kong laws, according to the Basic Law, Mr Hui quoted Mr Lu as saying. Mr Lu has refused to meet Governor Chris Patten, and few top government officials have met Mr Lu since a political row soured relations two years ago. But Mr Lu described his encounter with the Police Commissioner as a courteous meeting of ''good friends''. In another sign of close co-operation, it was revealed that a seminar would be held early next year to fight increasing drug trafficking across the border. The seminar, to be held in the first six months of 1995, would be organised by China's Public Security Bureau and anti-narcotics bodies and their Hong Kong counterparts, mainland police commissioner Zhu Entao said. Mr Zhu said he was very concerned about the dramatic increase - 142 per cent - in narcotics-related crime in Hong Kong in the first six months of this year. Most of the drugs came directly from the Golden Triangle, but some were smuggled through China's Guangxi and Yunnan provinces, Mr Zhu said. Mr Hui said the present channel of exchanges would be widened. China was planning to send police officers to Hong Kong to study public relations, regional command and control centres and computer systems.