Some security experts have expressed concern over the use of a contact-less chip that doesn't require contact with a scanner. The new passport can be read about four inches from a scanner.

Given the fast pace of technology changes, and the 10-year life of a passport, it's inevitable that the RFID chip will become hackable and that technology will be built to access it from long distances, said Bruce Schneier, CTO of Contact Counterpane Internet Security Inc., based in Mountain View, Calif. The new passport could eventually allow for surreptitious access and tracking, he said.

Schneier contended that the State Department could have used an RFID chip that requires contact with a reader. "I can think of no benefit for a contact-less chip," he said. "The question is, if there is no good reason for RFID, why are they pushing so hard for it?"

Other experts downplayed such potential flaws. "The only vaguely legitimate arguments I have heard against E-passports is that they might permit someone two feet away from you to learn that you are American and blow you up, or permit someone two feet away to learn whatever might be stored on the E-passport," said Michael Shamos, a professor who specializes in security issues at Carnegie Mellon University in Pittsburgh.

"It's a balancing of risks. The E-passport will be much more difficult to forge and thus ought to reduce the prospect of terrorists getting hold of valid ones," he said.