LA Times: Reporting from Washington — The Obama administration on Tuesday proposed renewable-fuel standards that could reduce the $3 billion a year in federal tax breaks given to producers of corn-based ethanol. The move sets the stage for a major battle between Midwest grain producers and environmentalists who say the gasoline additive actually worsens global warming. For much of the last decade, federal officials have touted the potential of corn ethanol as a substitute for gasoline and a …