The D.C. Public Service Commission yesterday gave mixed reviews to a Potomac Electric Power Co. proposal to implement energy management programs in the District, rejecting some multimillion-dollar programs and approving others designed to help defer construction of a costly new generating plant.

Pepco yesterday said the commission "basically endorsed the Pepco program," while the Office of the People's Counsel, which represents customers in rate cases, hailed the PSC's decision to "reject" Pepco's proposals.

Pepco is trying to shave a total of 440 megawatts off the maximum electricity usage projected for the early 1990s as a way to defer the building of a $1 billion plant. The programs the PSC approved yesterday will allow Pepco to achieve a reduction of 100 megawatts on its peak demand, rather than the 146 megawatts it wanted to conserve in the District, said spokesman William Jones. The cost of the approved programs is not yet known, he said.

D.C. People's Counsel Frederick Dorsey said Pepco's proposal, which would have cost D.C. ratepayers $44.2 million, was rejected because it was not cost-effective and would not avoid the construction of a plant.

"Pepco does not have to spend millions of dollars for customers to save money," said Elizabeth Noel, deputy people's counsel.

"There are some real things that customers can be doing that can save millions of dollars and permit Pepco to cancel a plant" at the same time, she said. Some of those actions might be the installation of energy-efficient technologies, she said.

The PSC also told Pepco it could not put the Washington Area Metropolitan Transit Authority onto time-of-use rates, or rates that charge more for electricity at times of the day when demand on the generating system is greatest. The rates vary by hour, day and season of the year, and are meant to encourage customers to shift their electrical consumption to slack periods of the day.

The transit authority had argued it could not adjust its Metro schedules to save money.

The PSC also rejected a Pepco proposal to initiate a voluntary program for residential customers who agree to have their air conditioners and water heaters cycled on and off for brief periods during times of greatest demand. The PSC said Pepco had not demonstrated the program was cost-effective.

Pepco may increase the number of commercial customers on mandatory time-of-use rates, but may only extend them to customers who use 100 kilowatts or more during times of peak demand.

Pepco had wanted to apply the program to smaller businesses. It will now be able to extend the rates to about 14,000 customers, rather than the 19,000 customers it aimed for.

Pepco will be allowed to initiate a voluntary program for large commercial and governmental customers who agree to cut their usage to a pre-determined level when the company requests it, but only after it recalculates the marginal costs associated with the program, the PSC said. Pepco has had customers on an experimental program of this kind.

Pepco has asked the Maryland Public Service Commission to approve the energy management plan, which, in conjunction with that for the District, initially carried a $98 million price tag. A Maryland decision is expected soon.