Photos and fingerprints are required of those visitors who must obtain visas to enter the United States - an expected 23 million arrivals in 2004.
Citizens from 28 countries, mostly in Europe, are exempt, according to the Department of Homeland Security, which runs the US Visitor and Immigrant Status Indicator Technology, or US-VISIT.
The new procedures comprise phase one of US-VISIT, a $380 million effort to track down suspected terrorists.
By 2005, every port of entry on land, sea and air will have the photographic and fingerprinting technology. All US visas and passports will eventually include photos and fingerprints - called "biometric identifiers".
The programme takes effect after the US raised its terror alert in December. Intelligence allegedly indicated that al-Qaida was planning to hijack airliners for a repeat of the 11 September 2001 attacks.
Top US officials headed to airports across the country to help launch the programme, including Homeland Security chief Tom Ridge who defended a policy that has been criticised by civil liberty groups and countries whose citizens have been affected.
Homeland Security Secretary Tom
Ridge says steps are unobtrusive
"One of the primary responsibilities of any government is to make sure that their borders are secure, and we're doing that with this programme," he told NBC television.
"I think it's very unobtrusive. It takes about 15 seconds and no one seemed to mind," he said.
"We want them (foreigners) to come to the United States to work and to visit and to study, but we also need to make sure that we have a record of who comes into the country and when they leave."
Inkless fingerprints and digital photos will add 10 to 15 seconds to the immigration entry interview, which now takes 60 to 90 seconds, a Homeland Security spokeswoman told AFP. If it causes backups, it will be up to each of the 115 US international airports to solve.
But civil libertarians and immigrants said the biometric identification system may be an invasion of privacy.
"It doesn't seem likely that we're going to catch any bad guys through this program, but it is likely that a lot of immigrants are going to get caught up in the bureaucracy," said Michele Waslin, a spokeswoman for La Raza, an advocacy group for US Latinos.
US has tightened airline security
in response to 2001 attacks
"It does appear to be a step toward creating a national registry," said Barry Steinhardt, director of the American Civil
Liberties Union's technology and liberty programme. "It is a tool for creating a surveillance society."
Last week, Brazil began fingerprinting and photographing US visitors in response to the incoming US security measures, after a judge said the American security procedures were reminiscent of Nazi policies.
"I consider the act absolutely brutal, threatening human rights, violating human dignity, xenophobic and worthy of the worst horrors committed by the Nazis," said federal Judge Julier Sebastiao da Silva.
Visitors from the following countries will normally be exempt from the stricter security checks: Andorra, Australia, Austria, Belgium, Brunei, Canada, Denmark, Finland, France, Germany, Great Britain, Iceland, Ireland, Italy, Japan, Liechtenstein, Luxembourg, Monaco, the Netherlands, New Zealand, Norway, Portugal, San Marino, Singapore, Slovenia, Spain, Sweden and Switzerland.