Garden apartments, businesses, a city health center and some 300 town houses will be built on the 25 acres in far Northeast that used to be the site of the old Parkside public housing project, the D.C. Department of Housing and Community Development announced yesterday.

The department said it will seek developers this fall for the project, at 701 Kenilworth Ter. NE. Some of the town houses will be reserved for lower-income families, while the others will be sold at market rates, according to a press release. Contruction is expected to begin by mid-1980.

The chosen developer will purchase the land for the city, build the homes, and be required to sell 30 percent of the town houses back to the city, with 15 percent of them reserved for rent and 15 percent for sale to low-and moderate-income families. Some of the garden apartments also will be available to lower-income families through rent subsidies.

Parkside, a 351-unit public housing project, was demolished in the late 1960's and early 1970's by the National Capital Housing Authority, which promised residents that a new housing project would be built. Housing director Robert L. Moore said priority for the new homes will be given to former tenants of Parkside.

The housing department also said that planning discussions are being held with the federal government about the Knox Hill site, another vacant tract at 2310 Ainger Pl. SE, where a public housing project once stood. Former tenants there also are to be given priority in the new development, the department said.