MORE women from China are becoming prostitutes in Hong Kong, but they will not be prosecuted because the Government does not regard them as doing a ''job''. ''The policy is that people who are found working will be prosecuted,'' Secretary for Security Alistair Asprey said. But he was quick to add that women from China who come to Hong Kong to be prostitutes do not fall within the prosecution policy. Illegal immigrants found working in Hong Kong are normally jailed for 15 months. According to police statistics, there was a sharp increase in the number of women illegal immigrants arrested from 5,935 in 1992 to 8,467 in 1993. ''Many of these females enter as wives of Hong Kong residents, to give birth or, increasingly, to work as prostitutes,'' Commissioner of Police Li Kwan-ha said in his written reply to a question raised by legislators. Legislators criticised the Government's laissez-faire policy and said it would encourage more prostitutes from China. Liberal Party legislator Miriam Lau Kin-yee said the Government was ignoring the rising trend. And United Democrat legislator James To Kun-sun described the policy as ''unthinkable''. ''We can say it is for humanitarian reasons that women illegal immigrants who come to give birth are not prosecuted,'' he said. ''But why doesn't the Government prosecute the prostitutes?'' Mr Asprey said the total number of prostitutes from China was far less than the 8,467 women illegal immigrants recorded last year. He said women illegal immigrants also worked in factories and other places. The Government did not intend to map out a special prosecution policy. ''We do not have and do not want to have a specific policy on female illegal immigrants,'' he said. United Democrat Martin Lee Chu-ming said at least the Government should ask them to pay tax. But, Mr Asprey responded: ''I am not responsible for the Inland Revenue Department.'' Deputy Secretary for the Treasury Kwong Ki-chi, taking up the question, said: ''I don't think these people will stay in the territory long enough to earn an income that exceeds the basic allowance.'' As for the general problem of illegal immigrants, Mr Asprey said prosecuting huge numbers would not solve the problem, and would increase overcrowding in jails. According to figures from the Correctional Services Department, prisons are 14 per cent overcrowded on average, with illegal immigrants constituting 26 per cent of the inmates. There had been a decline in the number of illegal immigrants arrested at construction sites, from 1,114 in 1992 to 573 in 1993. Police envisaged more would enter Hong Kong this year, but would be frustrated in finding jobs. The Government was adopting an even-handed approach to prosecuting both employers and illegal immigrants so as to frustrate employment.