The failure of the attempted Soviet coup is a victory not just for democracy, but especially for democratic federalism. While the junta attempted to seize power through Mikhail Gorbachev's central Soviet government, it was Boris Yeltsin, the democratically elected leader of the Russian Republic, who rallied the opposition.In Sinclair Lewis's novel "It Can't Happen Here," when a totalitarian regime seizes power in the US, virtually its first act is to dismantle the state governments that give our nation its name. Mark Menchik, Alexandria, Va. Letters are welcome. Only a selection can be published, subject to condensation, and none acknowledged. Please address them to "Readers Write," One Norway St., Boston, MA 02115.