Chesapeake & Potomac Telephone Co. yesterday offered its customers in the District of Columbia a tradeoff -- a reduction in basic monthly rates in exchange for a new charge for information calls.

A subsidiary of American Telephone & Telegraph Co., C&P asked the D.C. public service commission to approve a new fee for information calls that would permit three free directory assistance calls a month, after which each call would cost 20 cents.

C&P said each of the free calls would permit requests for two telephone numbers and emphasized that interstate long-distance information calls would not be charged under the proposal.

Although Bell System companies throughout the country have been seeking to install fees for information calls, C&P apparently is the first to offer reduced consumer rates in return. In other jurisdictions, according to AT&T officials, consumers should benefit from owner rates increases in the future.

C&P of Virginia received approval from the State Corporation Commission to begin charging for information calls last year. Effective Nov. 4, customers began paying 10 cents for every call after a monthly allotment of six free calls. The company said this would result in savings of $2.1 million.

In Maryland, C&P proposed informaation call fees but the legislature delayed any such charge fot at least a year from last April, pending a study by that state's regulatory commission.

Information call charges have taken effect in more than a dozen states to date but were rejected earlier by the D.C. commission. In Oregon, volume of information calls per day dipped to 80,000 from 181,000 after the charges began, C&P president Samuel E. Bonsack said in a recent interview.

If the information charge is approved, "it is expected that the volume of calls will be substantially reduced and so will the expense of providing the service," said C&P vice president Ralph W. Frey, who heads the company's District operations.

Basic monthly rates would be reduced by 41 cents for each main telephone, if the commission approves, according to C&P. This would be made possible by an expected 60 per cent reduction in information calls and a "significant reduction" in operators needed to handle such calls.

The company yesterday provided data showing that C&P in Washington now receives 24 million information calls a year and that the cost of providing such a service is $5.6 million annually.

C&P said less than 9 per cent of its customers make half of all information calls.

Under the C&P plan, handicapped customers such as blind persons and the physically disabled, would be exempted from the proposed charge. Other exemptions would apply to hospital patients, hotel and motel customers and coin telephone users.

"Considering the 41-cent reduction in monthly rates, a customer may make five directory assistance calls [three calls free and two at 20 cents apiece] and still pay about what the present charge for service is today," Frey said last night.

He added that C&P expects about 10 per cent of its District customers would have any information call fees.

C&P said if the plan is implemented, his firm would save $1.4 million a year based on estimated 1977 volume.