A group of D.C. consumers yesterday delivered the results of a two-year study of the Potomac Electric Power Co. and its energy forecasts, calling on the utility to rely more on conservation and less on costly construction to meet the city's energy needs.

While consumers have been conserving more and more energy, Pepco has overbuilt production capacity based on faulty forecasts of growth in demand, the 113-page report charged.

The Consumer Utility Board, which wrote the report under a federal grant and under the auspices of the People's Counsel of the District of Columbia, also recommended cost-benefit comparisons to determine if conservation measures such as home insulation might be more cost efficient than building new generating plants and called on Pepco to improve load management techniques.

Traditional concepts of energy conservation "have placed the burden of conservation solely and squarely on the shoulders of consumers," said Edward DeVaughn, vice chairman of the board. "Utilities must see conservation as a resource to be used instead of building new plants."

While Pepco users have reduced energy consumption by one third over last five years, Pepco has made four attempts to institute major price increases, the board said. What the board called on Pepco to do is to seek ways of conservation as seriously as they seek new capital for construction.

Pepco currently has 32 percent excess capacity, board member Anton Wood said. People's Counsel Brian Lederer said that Pepco's 10-year construction plan will cost more than $1.8 billion, and require rate increases to fund it.

Pepco denied charges that the utility has been badly off base in its forecasts and construction programs and noted that most of the construction expenditures projected will add nothing to the utility's generating capacity.

"Overbuilding is an old charge," said David Boyce, a spokesman for Pepco. "I think it's been disproven many times in the hearing room." Boyce said that current excess capacity stemmed from inability to predict the 1974 oil embargo. "It's an eight-to 12-year process to build a generating plant. In the late 1960's and early 1970's, we were building to meet a historic and present growth rate of 9 to 10 percent a year in demand," he said.

After the embargo, the rate dropped off, stabilizing at slightly under 2 percent a year. Building plans for the future are based on that rate of growth, he said. Boyce also said that projected construction expenditures of $1.8 billion have been reduced by $1 billion.

Boyce said Pepco officials had not been given a copy of the report, which was released yesterday morning in the District Building with copies presented to Mayor Marion Barry and council member Wilhelmina Rolark.

"basically, we'll be more than happy to look at their recommendations and adopt all those in the long-term interests of our customers," Boyce said.

People's counsel Lederer called the report "a major step in developing a local energy policy." Lederer said the board's work "addresses a sense of a lack of control . . . a concern over the futility of dealing with the problem rate case by rate case when the policy has already been set and the money spent."