The General Services Administration has announced an Aug. 24 sales date for the old federal building that was used as a staging ground for the Reagan Inaugural Committee in 1980.

Formally known as Tempo C, the building and 7.8 acres of property are situated at 2nd and Q Sts. SW. Over the past several years, the District has wanted the land for a new Metrobus garage. But changes in federal land disposal policies by the Reagan administration stalled the negotiations so long that the city lost interest.

The Smithsonian Institution also had sought the property, free, as a location for a new support facility for its museums. The Reagan administration turned down that request earlier this year.

Three other properties are on the market block:

* A building at 425 2nd St. NW on property known as Square 571 will be sold Aug. 31. The 1.16-acre parcel, with one building, is in an urban-commercial zone.

* Camp Simms Military Reservation, a 24.4-acre property in southeast Washington that will be offered Aug. 17.

* A portion of the old Wilburn Family Housing Annex to Bolling Air Force Base at 4th and Trenton Sts. SE will be sold Sept. 7 through an open-listing with area real estate brokers. The seven-acre property has two buildings in an urban-residential zone.