Alexandria Mayor Frank E. Mann and two local businessmen have fallen more than $24,000 behind in local real estate taxes on a piece of waterfront property they jointly own, making their partnership one of the largest delinquent tax accounts in the city.

Alexandria city records show that although the partnership has paid $40,000 in taxes since 1976, the partnership's periodic $500 payments are not keeping with the taxes and penalties assessed on the property.

The property is a piece of vacant land on the Alexandria waterfront that the mayor and his two partners, John C. Richards and Robert J. Sweeney, once hoped to convert into a motel and restaurant complex.

Asked for comment yesterday, Mann said, "I have nothing whatsoever to do with it directly. We had not been billed for several years, so we went to the city and asked them what happened. They gave us a lot of gobbledygook and then we received a tax bill."

But Mann said that by agreement of the partnership, listed in city records as The Port of Alexandria Co., Richards is responsible for the partnership's financial matters.

Richards said yesterday that the city failed to send him tax bills for the property for many years and that the current rate of payment was the suggestion of city officials. "It was their suggestion and we have followed that very diligently," he said.

City Manager Douglas Harman said, however, that while city officials may have agreed to the payment schedule, that arrangement does not clear a delinquent taxpayer or protect him from future legal action by the city.

City officials also contend that, under Virginia law, property owners are responsible for paying taxes whether or not they receive tax bills.

Richards said yesterday that when he owned the property by himself he had complained that it was overassessed to the Board of Equalization and Review, but that a decision had never been made on the matter. The board has power to raise or lower real estate assessments.

Alexandria records do not show, however, that Richards made a formal complaint to the board.

The city has lagged behind other Washington-area jurisdictions in using laws providing for sale of property on which real-estate taxes have not been paid for more than three years.

A test case is now in the Alexandria courts to see if the city can sell property whose real estate taxes have been in arrears for more than three years. If Alexandria wins, Harman says he will recommend to the City Council that the properties that owe the largest amount be sold, including that partially owned by Mann.

Mann said yesterday that he is in the process of turning over his portion of the partnership to his stepchildren.

City figures show that last year alone the tax assessed on the property was $5,038.30. Since 1974, the figures show, $24,736 in back taxes and penalties on the property have not been paid.

A report prepared by the Alexandria Finance Office that covers 1974 to 1977 lists the Port of Alexandria Co. as the seventh largest delinquent taxpayer in the city.