Potomac Electric Power Co. electrical workers are to vote today on a contract that would give them a 41 percent increase in wages and benefits over the next three years at a cost of $31.8 million to the utility.

In return, the union workers would give the company broad flexibility to change work rules to improve operating efficiencies.

Because labor costs account for only 9 percent of Pepco's overall annual expenses, utility industry analysts believe the settlement will have little effect on consumer bills. Fuel costs make up 42 percent and capital spending constitutes nearly 49 percent of the company's yearly budget.

Details of the tentative agreement between Pepco and Local 1900 of the International Brotherhood of Electrical Workers were released by the union yesterday in a 19-page report to its 3,500 members.

"We have done our best under the most difficult and trying circumstances to gain every possible concession, even though we were faced with a long and expensive list of takeaways," Local 1900's leaders said in a joint statement in the report.

"This package is not everything that we wanted, but it is a strong continuation of the course we embarked upon in 1979," when the IBEW began representing Pepco workers, the union officials said.

The officals urged their members to approve the agreement, partly because "the company will make no further meaningful concessions short of a strike" that could end with the loss of previous contract gains.

Pepco declined comment on the Local 1900 report, "because we do not want to interfere with the union's ratification process," one company official said. However, well-placed non-union sources who are familiar with the terms of the contract said the union's report essentially is correct.

The tentative agreement between Pepco and the union was reached at 12:30 a.m. Sunday, ending a series of often tense and heated talks that began Feb. 15. According to the Local 1900 report, the basic agreement includes:

* A 25 percent increase in basic wages over three years, which includes a 9 percent increase in the first year and 8 percent boosts in each of the remaining two years of the contract. Unionized Pepco workers now earn an average hourly wage of $9.76.

* A provision awarding an additional, one-shot, 3.3 percent increase to about 1,500 Pepco workers whose work responsibilities had been increased in the past without a comensurate increase in pay. This provision also wipes out all existing grievances stemming from job classification changes.

* Increases in pension, medical, life insurance and vacation benefits, mileage and meal allowances, and shift premiums, amounting to about 12 percent over the next three years.

* An improved sick leave plan that allows workers to carry over unused sick days from one year to the next, or be paid for a portion of those unused days.

The union said in its report that "a new procedure has also been negotiated for tracking duties and responsibilities added to jobs" as of June 1, 1982, when the new agreement would be in effect retroactively.

A reliable nonunion source who is familiar with the contract said yesterday the "duties and responsibilities" clause means the company "would not have to get union approval to make job changes the company may need to meet changing market conditions." The clause, which would stay in force for two years of the three-year agreement, after which it would be subject to review by both parties, "gives the company much needed operating flexibility," the non-union source said.

To further soften that major union concession, Pepco agreed to provide "lifetime job and pay security" to workers with 12 1/2 years' seniority, according to the Local 1900 report. That means "no employe with 12 1/2 or more years of continuous service can be furloughed or reduced in pay due to lack of work, or to plant closings, reorganizations, automation, etc.," the union report said.