ALBANY — Gov. Cuomo and Mayor Bloomberg announced legislation yesterday that will head off a threatened 12 percent rate hike for New York City electric customers.

The legislation, first reported by The Post last month, guarantees permanent property-tax abatements to local electric-generating companies, removing the basis for a little-noticed Federal Energy Regulatory Commission decision in January that could hike city electric rates by $500 million a year.

“This legislation is targeted to resolve the issues raised by FERC, and should give them no choice but to reverse their decision,” said Cuomo.

The legislation, which was quickly passed by the Assembly last night and will go to the Senate early next week, makes the property-tax abatements permanent.

“By amending the existing [temporary] tax benefits, we are removing any and all justification” for the rate hike, said Bloomberg.