THE STREETS and avenues of Washington are lined with proud houses and sturdy buildings whose beauty and utility have won them the right to outlive their generation and even their century. These bricks and stones are not only history you can walk through, they are lessons in how to live well at a low expenditure of energy.

The best of the homes, churches and offices built before our century were designed to be open to natural light through windows sited to the sun and to the prevailing breezes. They had front porches instead of air conditioning, plants instead of humidifiers, and gardens to cool hot tempers and temperatures.

Preservation Week is being celebrated by the National Trust for Historic Preservation today through next Sunday with a series of events, planned to show how saving buildings saves energy.

The Trust Headquarters, the McCormick Apartments at 1785 Massachusetts Ave., NW, will be open to the public for tours and a slide show from 5:30 to 7 p.m. Thursday. The former luxury apartment, whose most famous tenant was philanthropist Andrew Mellon, has been converted to offices. Refreshments.

The Preservation Shop, 1600 H Street, NW, will open its new quarters, selling architecture, antique, design and decorating books, posters and preservation themed gifts, from 9 a.m. to 4:30 p.m. Thursday. Free Preservation posters during the grand opening.

"Washington's Historic Neighborhoods: Capitol Hill, Dupont Circle, Takoma Park, Anacostia and LeDroit Park" will be discussed by community leaders at a lunchtime seminar at noon Tuesday, at the Pension Building.

Energy Conservation in Historic Structures" will be discussed by officials from the Heritage Conservation and Recreation Service, noon Wednesday, at the Pension Building.

Exhibits of early Chicago architecture, Westover Salon prints, Rood Creek mounds in Georgia and native American structures will be on display at the Pension building during the Preservation Information Fair Wednesday and Thursday, Slide shows about preservation and literature and information will also be given.

"Preservation: Reusing America's Energy," cosponsored by the National Trust and the Smithsonian Institution Resident Associate Program is the theme of a symposium Wednesday at 10 a.m. at the Smithsonian's Museum of History and Technology, ($30 fee for members of either group, $40 for others).

John Sawhill, deputy secretary of the U.S. Department of Energy, is the chief speaker.