Washington ? 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 percent 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 system the Pentagon agency calls Total Information Awareness.

That system already has raised privacy alarms on both ends of the political spectrum, and Congress in February barred its use against American citizens without further congressional review.

Conceived and managed by retired Adm. John Poindexter, the TIA surveillance system is based on his theory that “terrorists must engage in certain transactions to coordinate and conduct attacks against Americans, and these transactions form patterns that may be detectable.”

DARPA said the goal is to draw conclusions and predictions about terrorists from databases that record such transactions as passport applications, visas, work permits, driver’s licenses, car rentals, airline ticket purchases, arrests or reports of suspicious activities.

Other databases DARPA wants to access include education, medical and housing records and biometric identification databases based on fingerprints, irises, facial shapes and gait.

Georgia Institute of Technology researchers Gene Greneker, left, and Bill Marshall test their radar system that can detect people by their walk from 500 feet or more. They tested the equipment recently in Atlanta.

Poindexter’s plan would integrate some projects DARPA has been working on for several years, including gait research headed by Gene Greneker at Georgia Tech.

At a cost of less than $1 million over the past three years, he has been aiming a 1-foot-square radar dish at 100 test volunteers to record how they walk. Elsewhere at Georgia Tech, DARPA is funding other researchers to use video cameras and computers to try to develop distinctive gait signatures.

“One of the nice things about radar is we see through bad weather, darkness, even a heavy robe shrouding the legs, and video cameras can’t,” Greneker said in an interview. “At 600 feet we can do quite well.”

The radar detects small frequency shifts in the reflected signal off legs, arms and the torso as they move in a combination of different speeds and directions. “There’s a signature that’s somewhat unique to the individual,” Greneker said. “We’ve demonstrated proof of this concept.”

The researchers are anticipating ways the system might be fooled.

“A woman switching from flats to high heels probably wouldn’t change her signature significantly,” Greneker said. “But if she switched to combat boots, that might have a difference.”