When Frank Lloyd Wright was 7, his mother bought him a set of Froebel Blocks, small modular cubes with triangles for roofs.

In his autobiography he wrote, "A small interior world of color and form now came within the grasp of small fingers. . . Here was something for invention to seize, and use to create."

For the architect, the fascination of building in miniature is easy to understand-no worries about mortgages, libility insurance, leaky roofs or clients' demands. Only will it fall down? For the child, architectural toys teach basic lessons about space, color and shape.

At The Octagon, 1799 New York Ave. NW, through June 17 is a show of building toys-mid-18th-century doll houses to expensive Fischertechnik construction sets. Shown here are three:

Above right: Donald Meeker, executive secretary of the American Institute of Architects, builds with Castle Blocks from Manchester Center, Vt. The 119-piece set includes turned columns, finials, moldings from hard woods and a history of architecture.

Above left: Jeanne Butler Hodges, president of the AIA Foundation, which organized the show, leans over a miniature antique shop, lent by Mrs. Alexander Russell of Alexandria. It took her two days to polish all the tiny silver pieces.

At left: The North Church is made from 18,000 Lego blocks, interlocking units from Billund, Denmark. The name, according to the show's informative catalogue, comes from the Danish leg godt , which means "play well." The blocks were designed by Godfried Christiansen.

The Octagon is selling the architects' original designs in blocks via silent auction and bags of sand with plans for sand castles by Hugh Newell Jacobsen. The Washington architect built an elaborate sandcastle for the opening. CAPTION: Pictures 1, 2, and 3, no caption, Photographs by Harry Naltchayan The Washington Post