After decades of party-switching by Southerners abandoning the Democrats, a countertrend is emerging: Centrist Republicans alienated by ultraconservative Christians in the GOP are becoming Democrats. This year, three former Florida Republicans--economic conservatives but social moderates--are running for Congress as Democrats. Susan Munsey, executive director of the Cocoa Beach Area Chamber of Commerce, could win an open seat in the Cape Canaveral area. Hermine L. Weiner, president of the Palm Beach Town Council, is an underdog against incumbent Republican Representative E. Clay Shaw. The third Republican-turned-Democrat, former Palm Beach County Commissioner Ron Howard, is in a wide-open race for the Democratic nomination.