SOME $80 million is needed to replace mechanical parking meters with electronic models and pay-and-display machines over the next three years, the Government told legislators. The new devices protect against tampering, are more reliable and are easier to maintain. They will be operated by prepaid smart cards. In a separate government funding request, the Education Department wants $30 million to provide introductory Putonghua courses for primary and secondary students during the 1996 to 1998 summer holidays. It is estimated about 200,000 students will benefit from the proposed courses.