ELDERLY, disabled and long-term patients can look forward to exemption from paying hospital charges in proposals to change the system, according to Secretary for Health and Welfare Elizabeth Wong Chien Chi-lien. Mrs Wong told a group of medical social workers yesterday that the proposals in the consultation document on health would provide these groups with ''a certainty of exemption''. She said the proposals, published last week, suggested that public assistance recipients be fully exempted from charges. There are also plans to grant other groups a waiver - the level of which has yet to be decided but could be 50 per cent. Under the existing system, such people had to apply for waivers and did not know if these would be granted, Mrs Wong said. She felt Hongkong's seemingly fair system discriminated in other ways because the pay-back for low fees was long queues.