To the Editor:

As properties on New York City's Upper West Side become more valuable, developers are requesting variances to build larger structures, and local elected officials are calling for a moratorium on all new construction. Overlooked in this controversy is one of the most important issues that will affect the future quality of life on the West Side: the apartment mix in new housing.

Developers now build predominantly efficiencies, one- and two-bedroom apartments, and have ignored the less profitable market for three- and four-bedroom units. Families with larger space requirements either pay a premium for the few suitable pre-World War II apartments or are forced to leave Manhattan.

The city should revise its housing quality program to encourage the construction of larger units. The programs's present guidelines permit a larger building if developers include certain features such as plazas and public space in the building and provide the community with amenities such as improved malls or funds for low-income housing. In order to qualify for the housing quality program, a builder should be required to include a substantial number of three- and four-bedroom apartments.

An influx of families with children into one section of the city, coupled with an enlightened program on the part of the Board of Education, might bring middle-class children back to the public schools. Since 1980, seven sites between 87th and 97th Streets on Columbus Avenue have been developed. The apartment mix in these buildings is 248 units for the elderly, 60 efficiencies, 400 one-bedroom units, 472 two-bedroom units, 71 three-bedroom units and no four-bedroom units. Less than 6 percent of the new units are suitable for families with two or more children who wish to remain in Manhattan.