The first dozen rehabilitated units of about 125 houses and 175 apartments went on sale here this week in the midst of a dreary, dilapidated 18-square-block area north of the General Motors Corp. headquarters.

GM Chairman Thomas Murphy, whose organization spearheaded the rehabilitation effort, said prices for the units will range from about $50,000 for town houses to about $80,000 for detached houses.

Atending the opening of the three finished and redecorated sales models were Detroit's outspoken, power-brokering mayor, Coleman Young, and Housing and Urban Development Secretary Moon Landrieu.

Murphy and Young said the prices were higher than anticipated when the innovative -- and for Detroit, radical -- program was announced exactly two years ago. But the prices are comparable to those for similar units elsewhere in the metropolitan area, they said.

In fact, given features such as original oak flooring, pristine beveled windows and ornamental stonework, it is unlikely that any of the houses could be touched for twice the price if they were located in a "better" area 10 miles away in any direction. With a nod to the question of security, some of the units are being equipped with items such as steel doors.

One retired GM executive observed two years ago, when GM launched the rehabilitation program, that a scant decade earlier GM had declined to become involved in the neighborhood -- even to the extent of maintaining and cleaning sidewalks bordering its headquarters. The giant corporation always argued that it paid taxes for such services.

Murphy a devoted free-enterpriser who often has spoken out on the topic organizations in the private and public sectors as much as possible. GM is trying to determine if decay in neighborhoods can be reversed around its plants as well as its headquarters.

Landrieu did some political work Monday, the first day of sales, telling of the 2 million public housing units that are targeted for rehabilitation nationwide by the Carter administration at a cost of $10,000 to $11,000 for each unit. He also announced that $2.5 million would be spent on rehabilitating the decrepit 2,100-unit Herman Gardens public housing on Detroit's far west side.

Landrieu also told of a 20-month federal demonstration effort aimed at communities with populations of less than $50,000, where skills necessary for central business district development probably are not available.