The State Department said Tuesday that it's adding two security features to the new electronic passports that it will start issuing in December.
The announcement partially assuaged privacy advocates who feared the technology wouldn't protect travelers from identity theft or from people who aim to harm Americans traveling abroad.
"Is it a step forward? Yes. Is it foolproof? That remains to be proven," said Barry Steinhardt, a lawyer with the American Civil Liberties Union.
As a result of tougher post-Sept. 11 security requirements, all new U.S. passports issued by the end of this year are supposed to have a microchip containing the holders' name, nationality, sex, birth date, place of birth, issuing office and a biometric identifier - a digital photograph.
A tiny antenna embedded in the passport cover will allow remote reading devices to capture the data on the chip. Privacy advocates said anyone with a portable reader could remotely read, or "skim," a passport holder's personal information.
The State Department said its original proposal in February generated 2,335 comments that were overwhelmingly opposed to the technology because of concerns that terrorists could identify and target them as U.S. citizens.
So the new passports' front covers and spines will include an anti-skimming material that blocks the radio waves that could pick up the data.
They also will use Basic Access Control technology, which utilizes a kind of personal identification number that must be touched physically to unlock the data on the chip.
"It will not permit `tracking' of individuals," the State Department said in making the announcement. "It will only permit governmental authorities to know that an individual has arrived at a port of entry, which governmental authorities already know from presentation of nonelectronic passports."
The international standards for "electronic" passports were set by the U.N.-affiliated International Civil Aviation Organization, which has worked on standards for machine-readable passports since 1968. The State Department said Basic Access Control will soon be added to the ICAO standards.
Bill Scannell, a privacy advocate who founded a Web site that generated comments opposing the new passports, said Basic Access Control is an unproven technology that shouldn't be used in an identity document.
"We don't know what can and cannot be done with this technology," Scannell said.
Other countries are also switching to microchipped, biometric passports at the request of the United States. The Patriot Act says visitors from 27 countries whose citizens don't now need visas to visit the United States would have to get electronic passports by next October.
The State Department will test the electronic passports in December with government employees who use official or diplomatic passports for government travel. The U.S. traveling public is expected to start receiving new or replacement electronic passports in early 2006.
The e-Passport contains the holder's biographic information and a biometric identifier, in this case a digital photograph, embedded in a contactless chip set in the passport.
The International Civil Aviation Organization expects that machine readable passports will be universally issued by 2010, as a way to speed air passenger flows and reduce terrorism.
An October deadline looms for a requirement that Visa waiver travelers produce e-Passports upon entering the United States.
The agreement, which went into effect last year and is to last for 3½ years, gives U.S. authorities access to information about passengers on trans-Atlantic flights.