Aviation security is an administration priority, and analysts say the deadline extensions are evidence of how difficult it is to make the nation's air travel system secure. The introduction of biometric passports has been hindered by the number of countries involved and by disagreements over privacy, a problem that may impair the passports' effectiveness.

The countries with visa waivers are Andorra, Australia, Austria, Belgium, Britain, Brunei, Denmark, Finland, France, Germany, Iceland, Ireland, Italy, Japan, Liechtenstein, Luxembourg, Monaco, the Netherlands, New Zealand, Norway, Portugal, San Marino, Singapore, Slovenia, Spain, Sweden and Switzerland. Last year about 15 million people from those countries came to the United States.

By October 2006, the 27 nations must include the biometric chip in their passports, but it will only contain a photograph, not a fingerprint or iris scan, said Homeland Security spokesman Jared Egan.