Residents who have been trying to persuade the city to set aside 12 acres at the McMillan Reservoir for a neighborhood park filed suit last week in U.S. District Court to stop the city from moving forward with its plans for commercial development of the site.

In the suit, residents charge that the city has proceeded with plans to develop the property without first conducting historical and environmental studies on the land. They also allege that District officials acted improperly when they agreed to amend the city's comprehensive plan to allow the land to be commercially developed.

Last November, the D.C. Council decided that an unspecified portion of the site would be set aside for a park, and residential and commercial development would be allowed on the rest.

The battle over the 25-acre parcel of land in Northwest across from Children's Hospital National Medical Center has intensified in recent months as the date approaches when the District will be allowed to develop it commercially. The District bought it for $9.2 million in September 1987, from the federal government with the stipulation that it could not be sold for profit for at least three years.

Officials in the Office of the Corporation Counsel said earlier this week they had not yet read the lawsuit and therefore could not comment on it.