ALBANY New York's so-called millionaire's tax expires in December after three years. But advocates for the poor, for schools and other causes that will no longer be able to count on the tax revenue are still fighting for it to be extended further. They targeted Gov. Andrew Cuomo. A group called Community Voices Heard met Aug. 9 at the State University of New York at New Paltz call for a continued millionaire's tax. The tax actually required a higher income tax rate for New Yorkers beginning at $200,000 a year. The social service groups still have many supporters in the Democrat-led Assembly and in the Senate's Democratic minority. But the Senate's Republican majority that can block the proposal remains strongly opposed.