"airiness and crisp confidence"

The architecture of American embassies has been stuck lately in a predictable tug-of-war between a desire to express openness and an obsession, in an age of terrorism, with security. The design for the new U.S. Embassy in London, released Tuesday morning by the State Department, finds a novel way to move past that split and take diplomatic architecture into fresh territory.

Designed by the Philadelphia firm KieranTimberlake, the proposed building makes an argument that an American embassy should do more than simply symbolize transparency, which all too often means a facility wrapped in glass but secluded deep inside an impenetrable suburban compound. Instead it aspires to a different and broader set of values, primarily having to do with ecological responsibility and neighborliness within a tight urban fabric.

The design suggests that, rather than standing in for certain American virtues, what a contemporary U.S. embassy should be doing is behaving virtuously. KieranTimberlake, in a written description of its concept, refers to the range of positive ways in which the building will "perform," both as an example of sustainable architecture and as a piece of urban design.

Even as the design itself, for all its airiness and crisp confidence, is hardly radical from a formal point of view -- it consists of a cube sheathed in a shimmering polymer scrim and resting on a ground-floor colonnade of concrete pillars -- it represents a major shift in how we think about the role of U.S. government architecture, both at home and abroad. It suggests putting an emphasis on action instead of values, measurable behavior rather than symbolic gestures.