READING Ross Milburn's letter (South China Morning Post, August 17) reminded me yet again of what a 19th century place Hong Kong is in so many ways. He says ''If women are paid less it is because they are perceived as being less valuable employees . . . ''. This gives employers free reign to indulge their prejudices against women. When such sentiments are expressed against Chinese, Jews, blacks or any other section of society they arouse justifiable outrage. Mr Milburn's letter has been written with the arrogance of someone who knows nothing about the subject. If he had a genuine interest in income differentials in Hong Kong he would have armed himself with knowledge, not displayed such fearless ignorance. I suggest he read some of the Government's publications on wages and salaries, which list most job descriptions in most industries and the average monthly salaries for men and for women. (See for example Report on Half-yearly Survey of Wages, Salaries and Employee Benefits, vol. II (Detailed Tables). In every case where both men and women are employed there is a large discrepancy in the salary, almost always in favour of men. Mr Milburn believes that capitalism is the only fair system and that it allocates jobs and resources according to ability and punishes those who pay more for men than for women of equal ability. It seems to follow that virtually all industry in Hong Kong is being punished for its systematic discrimination against women. How strange that most of these firms remain in business and make profits. Can Mr Milburn tell us which employers have been punished? Or does he really believe that women have less ability than men in almost all jobs? If that is what he thinks he really does belong in the 19th century. The truth is that women are systematically paid less because of the very prejudices Mr Milburn so shamelessly displays, not because they do the job less well. This injustice will continue until the Government has the courage to make it illegal, and to enforce the law. JEAN HOPKIN Central