AUGUSTA – About 680,000 Maine electric customers who get service through the standard offer will see their rates rise next March, the Public Utilities Commission said Wednesday.

The utility-regulating agency said it has accepted bids for standard offer power supply for residential and small commercial customers of Central Maine Power and Bangor Hydro-Electric companies.

When combined with the two utilities’ delivery charges, prices will increase March 1 by about 9 percent for CMP customers and 10 percent for Bangor Hydro customers. The two companies are the largest transmission and distribution utilities in Maine.

PUC Chairman Kurt Adams said high natural gas prices resulting from Gulf Coast hurricane damage earlier this year are largely to blame for the higher standard offer prices.

Global market conditions have also been a factor in higher fossil fuel prices, and electricity supply in New England is dominated by natural gas and oil, the PUC said.

But the commission said standard offer price increases have been held in check because it locked in two-thirds of the supply when fuel prices were lower last year.

Maine Public Advocate Stephen Ward agreed, saying the rate increases are “bad news, but not nearly as bad as it could have been.” Ward said he has no plan to challenge the rates.

Ward credited the PUC for diversifying power supply purchases, which he said held down increases that could have been higher, and encouraged it to

do so in the future.

The PUC said the increases will affect about 565,000 CMP and 114,000 Bangor Hydro customers.

The standard offer is the default service for customers who don’t choose to buy service from a competing supplier. Electricity sales in 2004 to CMP and Bangor Hydro residential and small general service customers was 4.8 million megawatts hours. More than 99 percent of that load was supplied by standard offer service.