SAN DIEGO - A 150-mile power line proposed by San Diego Gas & Electric Co. to run through San Diego County's backcountry would only provide electric customers a fraction of the savings originally estimated, it was reported Thursday.

When the utility filed its application with the California Public Utilities Commission Aug. 4 seeking permission to build a $1.3 billion transmission line, SDG&E estimated the project would save California electric ratepayers $447 million a year, the North County Times reported.

But now, according to a Friday filing with the commission, SDG&E estimates the savings to electric customers around the state would total $85 million annually over the 40-year-life of the project - between 2010 and 2050, the newspaper reported.

SDG&E says the reduction resulted from earlier miscalculations about the cost of natural gas and about the efficiency of plants, as well as the erroneous assumption that some power plants would switch from natural gas to oil because of oil's lower cost, the newspaper reported.

Jim Avery, vice president of electric for SDG&E, said the utility is still refining its projections and expects to file in a couple of days another revision.

Regardless of what the final statewide figure comes to, he said he is sticking by earlier public statements that SDG&E customers collectively would save more than $100 million a year on electric bills if the line is built, the newspaper reported.

The proposed route for the 1,000-megawatt Sunrise Powerlink would run from El Centro to Imperial County, crossing the Anza-Borrego Desert State Park and slicing through Ranchita, Santa Ysabel, Ramona and Rancho Penasquitos.