The new rules reflect and incorporate those comments by building in safeguards to protect the passport information, according to the State Department. To combat data theft, the passport RFID chip must be held within about four inches of a special reader and the passport cover must be open.

The agency also noted that the RFID chips are not the same as those used for warehouse inventory tracking over larger distances and will not permit "tracking" of individuals. "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 -- with greater assurance that the person who presents the passport is the legitimate holder of the passport," according to the rules.

The RFID chips will store only information that is already printed on existing U.S. passports, including name, nationality, sex, date of birth, place of birth and a digitized photograph of the passport holder. Also stored will be the passport number, issue date, expiration date and type of passport.

The chip will also contain a secure digital signature that aims to prevent any digital data from being altered or removed, as well as a unique identification number for each RFID chip. The chips will not contain home addresses, Social Security numbers or other information that might aid identity theft.

Passports from different countries must adhere to standards set by the International Civil Aviation Organization (ICAO) to be interoperable worldwide. The ICAO has developed international specifications for electronic passports that call for a minimum capacity of 32KB for data storage, but the U.S. passports will include twice that storage capacity in case new biometric data, such as fingerprints or iris scans, is added in the future. Any such additions would be subject to public comment periods, the agency said.