WASHINGTON — The Obama administration is set to announce today new regulations that would force the average gas mileage of new cars and trucks to nearly double in the next 13 years.

The rules, first proposed last year, would require new cars and trucks to average 54.5 miles per gallon in combined city and highway driving by 2025, up from 28.6 mpg at the end of 2011. Administration officials revealed details of the rule on condition of anonymity ahead of an announcement expected later today.

Obama announced last year he had reached a deal with automakers to raise fuel-efficiency standards, saving drivers money at the pump and dramatically cutting heat-trapping gases coming from tailpipes.

The changes will raise new car prices, but the government says that will be offset by savings at the pump.