The Towers, a landmark luxury rental apartment at 4201 Cathedral Ave. NW, will be sold in January for about $41 million to a developer who plans to convert the 614-unit high-rise to condominum ownership the developer confirmed yesterday.

The two-building apartment was completed in two stages about 20 years ago by developer-owner Melvin Gelman, who died in August. It has been the subject of reports about sale and conversion to condominium ownership for several years.

The prospective purchaser, Dwight Mize, head of the Mize Co. of Texas Inc., said yesterday in Dallas that an agreement has been reached ona sale contract to be executed early next year.

Mize, a developer based in Riverside, Calif., also has a contract to purchase the 723-unit, 33-acre McLean Garden complex on upper Wisconsin Avenue NW. However, redevelopment plans of the current owner, CBI Fairmac Corp. have been stymied for years. A CBI spokesman said that the sale to Mize is being delayed while a tenant group is given an opportunity to purchase the complex for about $25 million.

A certificate of eligibility for conversion of The Towers to condominium ownership was obtained earlier, according to Mize, and would be part of the purchase agreement. Mize said normal D.C. procedures to sell the indicidual units would likely begin some time in 1979.

The average price per unit would be more than $65,000 which veteran realtor Joseph Kinsky, a tenant there for 12 years, said he considers "exceptionally high."

Kinsky occupies a one-bedroom Towers' apartment $330 a month, including heat and utilities. He said some of the large three-bedroom units rent for more than $700 a month. He also said the building now requires considerable maintenance and repairs.

An average selling price of more than $100,000 might be expected if the prospective purchaser makes major repairs and then offers units for sale in 1979.

In recent weeks, some tenants in The Towers reportedly have been looking at new houses in the area because of recurring reports that the Towers would be sold and converted to condo ownership.

A number of well-known Washingtonians have resided at The Towers over the years. But the premium apartment in the connected building was occupied by Mr. Gelman and his family. It is a customized two-story penthouse unit far larger than the average single house.

The Towers now is owned by Mr. Gelman's estate, a corporation he headed and a trust he had formed, Mize said.