PORTLAND – In another sign of tough economic times, Maine’s largest electric utility faces a record amount of unpaid bills totaling four times as much as the amount owed four years ago.

Customers owed Central Maine Power a record $34 million through March, and regulators worry that the figure will grow in the coming winter. In 2004, the cumulative balance of unpaid bills was $8.4 million.

The $34 million represents nearly 10 percent of the roughly $350 million that CMP takes in annually from ratepayers. While that share appears large, it includes many people who are only a month or so late on their payment and will become current, spokesman John Carroll said.

Unpaid bills aren’t a new problem. But in recent years, regulators have noticed that the number of customers disconnected for nonpayment has been rising slowly. At the same time, the amount of money owed, especially by CMP customers, has shot up.

Unpaid balances emerged as a growing problem after 2004, when higher electricity generating costs began pushing up rates. CMP’s residential customers saw overall rates rise from roughly 12 cents per kilowatt-hour in 2004 to nearly 16 cents today. Rates at Bangor Hydro-Electric Co. and Maine Public Service Co., which were already higher than CMP’s, rose more slowly through the period, but now exceed 16 cents.

The Public Utilities Commission allows electric and gas utilities to disconnect customers who don’t pay their bills. In winter, however, customers who agree to long-term payment plans have special protections.

The rise in unpaid bills has implications for all customers: Some of the debt utilities can’t recover could eventually be absorbed by other ratepayers.

At a meeting last week, PUC staff members and representatives of Maine’s electric and gas distributors agreed to share information to try to head off the problem. One initiative is to help vulnerable customers identify power-hungry appliances and manage their use of electricity.

Despite heightened public knowledge about energy issues, some people simply don’t understand why they’re using so much electricity, said Derek Davidson, director of the PUC’s consumer assistance division.

“We’re talking about the most vulnerable customers,” he said. “They don’t have an awareness. They’re not going to go to some Web site.”

Regulators and utility officials also worry that people who can’t afford to buy heating oil this winter will try to survive with electric space heaters, stove tops and ovens, threatening their safety and racking up bills they won’t be able to pay.