UPDATE 1-U.S. energy regulator rejects plan to aid coal, nuclear

(Adds details, quote from FERC and Energy Secretary Perry)

WASHINGTON, Jan 8 (Reuters) - The U.S. power grid regulator on Monday rejected a directive by Energy Secretary Rick Perry to prop up aging coal and nuclear power plants, but said it had embarked on a new process to determine whether the grid can be strengthened.

The move was a blow to Perry who wanted the Federal Energy Regulatory Commission (FERC) to reward certain nuclear and coal-fired power plants that store 90 days of fuel on site for contributing to the reliability of the power grid.

President Donald Trump promised to aid the coal and nuclear industries, which have suffered shutdowns resulting from a glut of cheap natural gas.

In its decision, FERC said Perry's proposal to subsidize these plants may not be fair. "The record... does not demonstrate that such an outcome would be just and reasonable," FERC said in the filing.

FERC's new plan involves asking grid operators to submit within 60 days their concerns about the resiliency of the power system. The commission will then decide whether additional action is warranted to address grid resilience, FERC said.

Perry's directive, which was issued in September, came under harsh criticism by an unusual combination of natural gas, drilling, and wind and solar power interests who said it could hurt their industries and stifle innovation to improve power plants and the grid.

Consumer interests had also slammed the plan saying it would have spiked power bills for homeowners and businesses.

Perry said in a statement after FERC's ruling that he appreciates FERC's "consideration and effort to further assess the marketplace distortions that are putting the long-term resiliency of our electric grid at risk."

(Reporting by Timothy Gardner; Editing by Lisa Shumaker)