HARTFORD, Conn. — The supply of electricity this summer will be adequate in the Northeast even if the region experiences prolonged heat waves or power is interrupted, a nonprofit group that promotes power reliability said Tuesday.

In addition, electricity use is expected to rise as the economy continues to improve, the Northeast Power Coordinating Council said.

Nearly 3,500 megawatts of new capacity have been added since last summer and 1,200 megawatts are expected to be in service during the summer, the group said. Its coverage area includes the six New England states, New York and the Canadian provinces of New Brunswick, Nova Scotia, Ontario and Quebec.

The New York-based organization said peak demand for electricity this summer will be higher than last year in New England and Quebec, but lower in New York and Canada’s Maritime Provinces. Demand is expected to be unchanged in Ontario.

The forecast reflects a gradual economic recovery, offset by conservation, efficiency and other factors, said Edward Schwerdt, president and chief executive officer of the Northeast Power Coordinating Council. The council said it expects to have more than 1,800 megawatts of additional generating resources since last year. As the economy strengthens, more homes are built and businesses reopen or lengthen their hours of operation, leading to higher electricity use.

Schwerdt said the increase in generating capacity is “comfortably more” than the rise in expected electricity demand.

A broad range of assumptions were analyzed, including extreme weather conditions observed over 40 years, unexpected plant outages, transmission problems and other issues, the power group said.

It defines extreme weather conditions as widespread and prolonged heat waves with high humidity and near-record temperatures. Severe system conditions are considered to be transmission delays, outages and other problems.

The group said operating procedures and programs to keep electricity supply and demand in balance in the New York City area and New England would be anticipated only in the “unusual situation where a severe set of system conditions and extreme weather occur at the same time.

The assessment mirrors a similar forecast by ISO-New England, which operates the region’s electric grid. It said last week that the improving economy is expected to lead to more electricity use this summer, but the region should have enough power to meet rising demand.