Tens of thousands of District tenants may have been overcharged by their landlords during the last eight months because of computational errors by the D.C. commission charged with regulating rent increases in the city.

The admission has come to light in a report drafted for the commission that recommends it approve a reduced schedule of rent rises for this coming year to compensate for the rent increases allowed in June.

The estimated amount by which tenants may have overpaid their rents ranges from a few dollars to $15 a month, one source said. The total amount of the overcharge may run well into the hundreds of thousands of dollars.

Efforts to redress what the staff sees as a mistake are being held up by angry landlords who are members of the commission.They are boycotting commission meetings because they question whether an error was made. Under the city regulations, without at least one of the three landlord commission members present, no vote can be taken.

Most of the landlords who own the 112,000 rental units governed by rent control in the city may be adversely affected by the proposed changes in the complicated schedule of rent increases approved by the commission last year, according to a spokesman for the city's landlord association.

The mistake is blamed by one commission source on an "inexperienced staff" that made faulty calculations in determining how much of an increase in operating costs landlords experienced last year.

The draft report said that while the raw information used to compute those operating cost increases was correct, "in many instances it was misinterpreted or miscalculated."

As a result, operating costs were inflated by 64 percent, according to the report.

"Many, possibly most, of the rent increases authorized . . . were too large" the report said.

The mistake was found when the staff examined last year's report after an economist, who later was hired to work with this year's staff, challenged the operating costs used in compiling the report.

"Last year we didn't verify the data," said commission chairman Jerome Shuman. "This year, we had them (the staff) footnote the data because we wanted to make sure we don't have policy decisions based on error."

The draft report has thrown the city's already troubled nine-member Rental Accommodations Commission, whose rent increases automatically go into effect unless the City Council acts to change them, in further turmoil.

Members of the commission said a dispute has already arisen over exactly how landlords are to compute the fuel oil increases that were allowed to be implemented this month to cover skyrocketing heating bills.

Landlord members, already worried by what they saw as an insufficient increase in rent rises allowed in June, were quick to criticize the admission of error.

In a letter of resignation from the commission that he sent to the mayor Dec. 19, landlord representative Frank Emmet called this year's annual report "a travesty."

In an interview, Emmet, who said he withdrew his resignation at the request of Mayor Marion Barry, called the admission "laughable." He charged that many operating costs were ignored in the revised figures. "The annual report ought to be given to an independent auditor," he said.

Emmet, who heads a management company, said that before he begins to attend meetings of the commission again, he will wait "for further word from the mayor on my recommendations."

Landlord commission member Patricia Wells said she, too, has concerns about the accuracy of the draft annual report.

She said that a majority of the other members of the commission probably would vote to approve the recommendations if a landlord member appeared at a commission meeting as "a warm body."

"Don't you think it would be sheer stupidity for me to show up?" she asked.

She called the commission "a waste of the taxpayer's money."

Marie Nahikian, a commission member representing tenants, conceded that the agency has problems but blamed some of them on the landlord representatives.

"They have to realize the rent control commission is not the place to argue over whether or not you like rent control," she said.

As for the persons boycotting meetings, she said, "Commission members have got to realize the only way to work out differences is to be there (at commission meetings)."

The commission expected to vote on the final report earlier this week, but when it became clear no landlord members would attend, the meeting was postponed until next week.

As proposed in the draft report, the improperly high rent increases authorized last June would be corrected beginning in June.

At that time, landlords would begin calculating the amount of rent increases they can charge based on the rents they charged prior to the levying of the incorrect rental hikes. To do so, they would use a revised schedule for the current year -- corrected for the errors now in existence -- plus the new schedule for June 1980 to May 1981.

At least one tenant activist in the city thinks rents should be adjusted now to correct the error. "The commission admits there were errors made," said Evelyn Onwauchi, a housing counselor. "They should make the corrections now. Why should we continue to be overcharged?"