BOSTON – New England’s failure to build new electricity generating plants will put the region at a higher-than-usual risk of resorting to precautions this summer to keep its power grid from overloading, an organization that oversees the grid said Wednesday.

Compared with New York and parts of eastern Canada, New England faces a greater likelihood of measures to ease the load, including temporary voltage reductions and supply interruptions to certain industrial customers, the Northeast Power Coordinating Council said.

The New York-based council is one of eight regional organizations in North America that oversees grid reliability. The council’s territory – much of which was hit by a massive blackout on Aug. 14, 2003 – includes the six New England states, New York, and eastern Canada’s Ontario, Quebec and the Maritime Provinces.

The group said power supplies are expected to be adequate this summer under normal weather conditions across the council’s territory, which is home to 56 million people.

But the council’s annual summer forecast highlighted the tight electricity supply in New England, and cited the Boston area and southwestern Connecticut as problem spots because of local transmission bottlenecks and thin capacity.

New England has recently done less than other areas in the council’s territory to expand capacity. The region is forecast to bring online 26 additional megawatts of capacity this summer compared with last summer. In contrast, New York added 500 more megawatts, with Quebec adding 507 and Ontario 118. One megawatt can supply 750 to 1,000 homes.

“The need for additional resources in New England is fast approaching,” Edward Schwerdt, the council’s executive director, told reporters in a conference call.

Rolling blackouts have never before been imposed in New England to prevent longer and more widespread power outages, and council officials didn’t suggest Wednesday that such a step was imminent.

But they did cite an increased summer risk of precautions including curbing power supplies to industrial and commercial customers whose contracts allow for electricity interruptions. Other measures that could result from a prolonged heat wave include reducing voltage by 5 percent – a step that would have little or no effect on most home appliances – or relaxing requirements that supply reserves be maintained in case a generating plant suddenly fails.

Such precautions aren’t unprecedented in New England. ISO New England, the region’s grid manager, took such steps on three days last year, for example, and imposed a voltage reduction in the summer of 2003. In most cases, such steps go unnoticed by consumers.

The council’s report said a lingering transmission bottleneck in densely populated southwestern Connecticut “again has the potential to create reliability concerns.”

Projects to help ease the bottleneck are expected to be completed starting this year through 2009.

Boston’s system reliability is expected to improve because of a project by the utility NStar that’s scheduled to be finished in June. The project is designed to channel 24 percent more power into the city in case of an emergency.

The council also said power supplies could fail to meet demand in case of heat waves this summer in New York City and Long Island, although the risks there are less severe than in Boston and southwestern Connecticut.

ISO New England on Wednesday reiterated the need for more generating plants in a region where the such projects often face local opposition.

“Without new investment in power infrastructure and greater energy efficiency and conservation, New England could soon be consuming more electricity than it can produce or buy from its neighbors,” said Stephen Whitley, ISO New England’s chief operating officer.