WASHINGTON – Federal regulators agreed Wednesday to delay a new electricity rate plan for New England until late next year and will hear arguments on the embattled plan next month.

The decision comes after mounting criticism from governors, attorneys general and other elected officials, who contend the ISO New England proposal will boost prices by up to 24 percent but won’t guarantee the creation of more power.

Kurt Adams, chairman of the Maine Public Utilities Commission, estimated last month that the rate hike could cost Maine consumers $900 million over the next five years, representing an increase of 20 percent in the average homeowner’s electric bill.

In an order issued Wednesday, the Federal Energy Regulatory Commission said the rate changes in the “Locational Installed Capacity Proposal,” if they are approved, would not begin until October 2006. And, in response to requests from Connecticut, Massachusetts, Maine, New Hampshire, Rhode Island and Vermont, FERC will hear oral arguments in the case on Sept. 20.

“At a time when energy prices are already stretching family budgets, LICAP would impose a disproportionately expensive charge on New England electricity consumers,” said Rep. Rosa DeLauro, D-Conn.

And Rep. Edward Markey, D-Mass., added that at the September hearing, “FERC will hear some compelling arguments against LICAP, and I hope they will consider the harm this proposal would inflict on the entire New England region very, very carefully before they move forward.”

The plan would set up separate pricing regions, and the extra fees from the LICAP plan would be funneled to power companies as development incentives. Southwestern Connecticut and the Boston area have been identified as regions that need power transmission upgrades. Maine officials have said that up to 1,500 jobs in their state could be lost as a result of the decrease in consumer spending resulting from the rate hike.

FERC said that ISO New England would need a decision by Sept. 15 in order to implement the new rating system by Jan. 1, as originally intended.