Eight preservation awards will be given tonight by the Washington Metropolitan Chapter of the American Institute of Architects. Awards will go to small projects as well as important restorations. No awards were given for restoration of structures to be used as single-family houses, though three of the buildings started out as residences.

Two first awards go to Georgetown University's Riggs Library and the American Society of Landscape Architects headquarters. Merit awards go to the Old Post Office Building, the National City Christian Church and the Annex/Embassy Condominium. Citations will be awarded to the Mary McLeod Bethune Memorial Museum/National Archives for Black Women's History, and the Madison National Bank.

Georgetown University's Riggs Library (Healy Building, 37th and O sts. NW) by Michael Finch of Environmental Planning & Research Inc., is a classic restoration job. Only buildings that survive with their glories intact, though tarnished, such as this exuberant late Victorian interior, deserve this respectful historical research and restoration.

Paul J. Pelz (architect of the Library of Congress) designed the Riggs library in 1889-1891. Its four stories around a glass-roofed cortile (interior court) were filled with real gold leaf (none of your radiator paint), which has been restored.

Restored as a repository for rare books and intimate entertainments, it is now a magnificent vitrine or curio cabinet.

The gas light fixtures, lost in misguided electrification, were reproduced. The glass roof, unfortunately, was not retained but a day lighting effect was added above the glass ceiling. The mosaic tile floor, beyond repair, was carpeted. Victorian polychrome has been used to bring forward good details and paint out unfortunate ones. Lackey Construction Co./Hudson Shatz were the contractors.

The American Society of Landscape Architects Headquarters, designed by Royce LaNier and Ted Goldberg of Design Environment Collaborative, was remodeled from an heirloom left over from Dupont Circle's magnificent mansions and tasteful townhouses of 100 years ago. This building at 1733 Connecticut Ave. NW and its two neighbors were designed by B. Stanley Simmons, an architect who liked H.H. Richardson's wide-mouth doorways and Beaux Arts ornaments.

For 15 years, after a millinery shop gave up when women stopped wearing hats, the property sat empty. The landscape architects undertook a careful restoration of the facade and the interior. A fifth floor was hidden behind the mansard roof.

When it was finished, a fire gutted the work, charring the meticulously restored woodwork. The owners, 1733 Associates, and the architects had it duplicated by the contractor Columbia Construction Co.

Today, with the dirt cleaned out of its elaborate stonework wrinkles, it presents a Richardsonian smile to the avenue.

The Old Post Office, the most extensive, expensive and visible remodeling project in town, won merit awards for architects Arthur Cotton Moore/Associates in a joint venture with McGaughy, Marshall, McMillan, Stewart Daniel Hoban, Inc. and Associated Space Design, as well as historic consultants Preservation Urban Design Inc., contractor Grunley-Walsh Inc. and its owner, the General Services Administration.

Possibly only the former General Service administrator Jay Solomon would have had the courage to commission such an imaginative reordering of vast open space as Moore has designed. As a result this month or next, the National Endowments for the Arts and the Humanities will have splendid offices that reflect their missions. Next year, the public will have a new shopping and dining mall, and, on April 19, 1983, a spectacular bell and observation tower.

The National City Christian Church on Thomas Circle won merit awards for architects Walton-Madden-Cooper and Schoolfield Construction Co. Inc. for incorporating new lighting, sound and climate control systems without disturbing the 1929 neoclassical building designed by John Russell Pope.

A mansion at 1706 New Hampshire Ave., designed by George Oakley Totten, architect of the grandiose 16th Street palaces built by Mary Henderson, has been born again as an office building. Merit awards for the respectful restoration, went to the architects Archetype; the consultants, Sibley Jennings and Brian H. Ford; the owners, Gaspey Associates, and the contractor Anglemyer Construction and the Resolute Corp.; as well as Malcolm Robeson for the marbleizing and Randall Edwards for the wood restoration.

Two other Totten houses at 2100 and 2108 16th St. NW won merit awards for an unexecuted project for architects Jerrily R. Kress and David Cox, as well as the owners, McCulloch Development Corp.

Mary McLeod Bethune Memorial Museum and National Archives for Black Women's History, 1318 Vermont Ave. NW, won a citation for its owner, the National Council of Negro Women, its architect, William Ward Bucher and Associates and construction manager Terrance Lamb.

A citation went to the brand new Post-Modern Madison National Bank Building at 2833 M St. NW, architects Martin & Jones, and Sigal Construction Corp.