In an oversight that one city councillor described as a "colossal mistake," Cambridge overpaid its mayor by more than $30,000 during the past three years.

Mayor Kenneth E. Reeves '72 admitted Monday that he has been paid a $13,000 annual stipend for serving on the Cambridge school committee, even though the mayor's yearly salary--now more than $44,000--had been adjusted in 1988 to include that stipend.

In other words, he got the stipend twice.

The mayor immediately promised Monday that he would return the funds to the city.

Reeves said he only became aware of the overcompensation last Friday, when questioned by the Cambridge Chronide.

"This has just come to my attention, and I am very sorry to learn of it," he told the city council on Monday.

"I never once saw one of those checks; they were deposited directly to my account," the mayor said.

While city officials said the oversight was an honest mistake, the fact that it lasted six years has raised serious questions about Cambridge's massive bureaucracy.

"It is regrettable, and it is certainly disappointing, that a situation like this could go on so long," Councillor Francis H. Duehay'55 said last night.

Since 1982, the seven members of the school committee--including the mayor--have each received a stipend, now $13,000 per year, for their work.

Six years later, in May 1988, the city added $10,000 to the mayor's annual salary as compensation for the school committee seat.

But the mayor's stipend was never deleted from the school committee budget, and the committee said it was never told of the 1988 ordinance.

"We were doing what we believed was normal practice," said James R. Ball, the public information director of the school department.

"We had never been notified that there was any change in the arrangement we'd been doing since 1982," Ball said. "This never came to anybody's attention before last Friday."

A copy of the school committee's fiscal 1994-95 budget obtained by The Crimson still includes a salary item for $91,000--or $13,000 for each of the committee's seven members, including the mayor.

Ball said the oversight was not detected prior to last week because Reeves' predecessors, Alfred E. Vellucci and Alice K. Wolf, had turned down the stipend, and the money had been returned to the committee.

Wolf refused the stipend, she said, because she was the author of the proposal that enabled the school committee to pay its members. Vellucci said he had the money donated to purchase violins for Cambridge public school students.

Wolf said yesterday that she had understood the mayor's salary, after 1988, to include the compensation.

Vellucci agreed. "Evidently [Reeves] must have made a mistake," Vellucci said last night. "He probably didn't know that."

Ball said the oversight began in October 1992 when Claire E. Rodley, the school committee secretary, informed Reeves that he not been receiving his stipend since he took office in January.

"A check was then issued to me, retroactively paying me the salary I had not received, and a check was issued to me each week thereafter until I discovered the error," Reeves said Monday.

Rodley defended her mistake yesterday. "Other mayors had been paid," she said. "To the best of my knowledge, he was entitled to be paid the same as the mayors before him."

Ball also defended Rodley's actions.

"The city council may have voted on the increase, but the school committee never received a paper saying, 'Stop paying the stipend," Ball said.

Reeves said he had noticed the difference on his W-2 tax forms between his salary and that of the other eight councillors. But he said he assumed the difference was equivalent to the value of his Ford automobile. The car is provided by the city for the mayor's use, but is subject to taxation.

Reeves said he asked City Manager Robert W. Healy to investigate the overcompensation last week.

"I must unequivocally state that at no time have I been aware that I have been paid more than was due to me," Reeves said Monday.

City officials yesterday criticized a bureaucracy that allowed two salaries to exist for one job.

Alfred B. Fantini, a school committee member, said the city auditor should have detected the mistake years ago.

"It's probably embarrassing to say, but it fell between the cracks," Fantini said yesterday. "There's a checks-and-balances that needs to take place in the city auditor's office that doesn't take place."

James Conry, the school department's finance manager, did not return repeated phone calls yesterday.

But others said budget mistakes are almost inevitable.

"It's a very bizarre history, this whole thing,"Councillor William H. Walsh said yesterday. "I don't think it's as clear an overpayment as it would seem."

Walsh said that at one point in the mid-1980s, the mayor received three separate school salaries.

"If it's an error, it's really an error of confusion," he said.

Vellucci also said he was willing to give Reeves the benefit of the doubt.

"Lessons are learned by mistakes," former Mayor Vellucci said.

City officials insisted that the overlap of both budgets will be corrected.

"It must be rectified," Duehay said. "I'm sure by the time the next budget comes up, [the stipend] will no longer be in there.