Christy MacLear, executive director of Philip Johnson's Glass House for the National Trust, recognizes the unprecedented nature of the project, but finds it neither sad nor daunting. Ms. MacLear has had to face two major challenges: how to keep something that was always on the lively edge of the new from becoming a lifeless simulacrum, and the even more difficult problem that goes straight to the heart of the matter -- how to deal with a period and a style for which no models exist and standards are only evolving at a time when the modernist architecture of the 20th century is being rapidly and thoughtlessly demolished. Obviously, the Glass House could not follow the formula of a tastefully reinvented past. You can't reinvent Philip Johnson.