In Reversal, Rowland Vetoes Bill to Cut Emissions at 6 Power Plants
Gov John G Rowland vetoes bill that would have forced Connecticut's six oldest and least efficient power plants to cut emissions of smog-forming sulfur dioxide and end plants' ability buy federal emission credits from other, cleaner plants in Northeast; says bill, which he earlier said he would sign, would worsen state's air quality on smoggiest days and leave state open to California-style power shortages this summer; Democrats and environmentalists say veto show Rowland cares more about power-industry profits than clean air (M)