Armed with a new $126,000 federal grant to analyse the potential for local electric power conservation and the rate structure of Potomac Electric Power Co., the city's People's Counsel yesterday asked for a postponement of hearings on the utility's request for a $45.5 million rate boost.

Brian Lederer, who recently took over as the D.C. People's Counsel, said the federal Department of Energy has awarded his office a contract that provides for "major citizen" involvement in monitoring a rate increase proposal.

The nine-month study, already in progress, is the first financed with federal money to seek a broad analysis of costs and benefits to a particular community from various options for the future.

Lederer, a Washington lawyer who was active in the political campaigns of Sen. George McGovern (D-S.D.) and President Carter, said he submitted a proposal for the study to the DOE soon after being nominated by Mayor Walter E. Washington as the city public's representative in rate cases before the Public Service Commission.

The local analysis will be similar to a citizen study conducted in Seattle, where the City Council concluded that a program of conservtion measures would be more efficient in meeting future power needs than participating in construction of new power generating facilities, Lederer said.

In a petition filed yesterday with the D.C. Public Service Commission, Lederer said Pepco received a $29.4 million rate boost late last year and that a delay in considering the full increase now being sought would not be harmful to the company.

Specifically, Lederer said he would not oppose hearings for about $19 million of the rate increase now being sought, because current rates are not bringing in the amount of revenues Pepco is permitted.

But he suggested a postponement for nine months, until the study is completed, on about $25 million of the higher rates proposed by Pepco. This portion of the rate increase is largely attributable to construction to meet future power needs. Lederer said the need for such spending would be a primary focus of the current study.

When completed, the report is expected to indicate how Pepco can forecast its need for generating facilities more reliably, how Pepco's construction timetable and type of generators can reflect the "lowest possible cost and maximum use of existing capacity and facilities," alternatives could reduce construction programs, Lederer said.

Faulty forecasts of the need for power here have resulted in "rate instability which threatens the financial integrity of the power company and has further caused a devastating ripple effect upon the entire economy of D.C," a statement by the People's Counsel office charged.

To back up that claim, Lederer noted that Pepco has received five rate increases in the District since 1970, totaling $109.2 million (not counting higher revenues associated with fuel adjustment clauses).

The People's Counsel proposal is based on the current status of Pepco as a firm with excess power production capacity-which resulted from slower-than-anticipated growth in local consumption during and after the recent energy crisis.