(Troutdale, OR)  --  A proposal for a penny-a-gallon gasoline tax in Troutdale is leading in initial returns.  The tax, which would be phased in over three years, is ahead by a 53-47-percent margin.  So far, about two-thirds of those voting in the Riverdale School District are favoring a five-year local-option levy to fund operations.  It would mean a dollar-37 for each one-thousand dollars in assessed value.