Nuclear power is regaining favor as an alternative to other sources of power generation, such as coal-fired plants, which have fallen out of favor because they are major polluters. But the high cost could lead to sharply higher electricity bills for consumers and inevitably reignite debate about the nuclear industry's suitability to meet growing energy needs.

Nuclear plants haven't been built in meaningful numbers in the U.S. since the 1980s. Part of the cost escalation is bad luck. Plants are being proposed in a period of skyrocketing costs for commodities such as cement, steel and copper; amid a growing shortage of skilled labor; and against the backdrop of a shrunken supplier network for the industry.

The price escalation is sobering because the industry and regulators have worked hard to make development more efficient, in hopes of eliminating problems that in the past produced harrowing cost overruns.

Today, 104 nuclear reactors are operating in the U.S. Most are highly profitable but that was not the case until fairly recently. Moody's worries that continued cost increases could weaken companies and expose consumers to high energy costs.

Many utilities said they are watching with interest. Ralph Izzo, chief executive of Public Service Enterprise Group Inc. in New Jersey, said his company may not be big enough to build a nuclear plant, even though it is a nuclear operator. ''We're concerned by the rise in construction costs,'' he said.