WASTE management contractors last night blasted a government plan to charge for dumping at landfills, calling it ''archaic, arbitrary, discriminatory and illogical''. In a letter sent to politicians, the Environmental Contractors Management Association accused the Government of ignoring its views. ''Since it is our members who collect solid waste and transport it to the landfills, it is our members who will have to actually pay the charges and to try to recover those charges from their customers,'' said the association, which claims to represent the majority of waste management contractors in Hong Kong. The plan to charge private waste collectors is to take effect on December 7. Charges will be $175 per vehicle with a payload of less than five tonnes, and $350 per vehicle for more than five tonnes. Dumping of waste at landfills now costs nothing. The association said although it agreed with the ''polluter pays'' principle, the proposed system was flawed. It said the charging scheme with a break point at five tonnes of payload was ''arbitrary, irrational and discriminatory'' because it did not take into account the types and sizes of vehicles used to collect waste. And requiring dumping tickets to be prepaid would mean higher administration costs for members and would require more government staff at landfills. The association said it was ''discriminatory'' that Urban Council and Regional Council collectors were exempt from the charges. An Environmental Protection Department spokesman last night said that despite Executive Council approval, the plan was being revised.