WASHINGTON (AP) - Watch your step! The Pentagon is developing a radar-based device that can identify people by the way they walk, for use in a new antiterrorist surveillance system. Operating on the theory that an individual's walk is as unique as a signature, the Pentagon has financed a research project at the Georgia Institute of Technology that has been 80 to 95 percent successful in identifying people. If the Defense Advanced Research Projects Agency, or DARPA, orders a prototype, the individual ``gait signatures'' of people could become part of the data to be linked together in a vast surveillance...