A senior U.S. official says steps are moving forward to implement a new sophisticated data program aimed at ensuring that persons who are security risks cannot enter the United States.

As part of changes implemented by the Department of Homeland Security, in response to the September 11, 2001 terrorist attacks, the government has been implementing a new program called "US-VISIT."

It employs sophisticated digital fingerprint scanning and information processing techniques, known as "biometrics," that are designed to help prevent individuals with criminal histories or those who are security risks from entering the country.

Asa Hutchinson, undersecretary for border and transportation in the Homeland Security Department, says the program has already had successes.

"It is a historic achievement in which we, for the first time in history, can use a biometric ability to confirm the identify of those traveling to our country with visas," he said.

US-VISIT is currently deployed at 115 airports and 14 seaports. Eventually, all visitors will have a special "scannable" passport. Those not from countries with "visa waivers" will have to be photographed and fingerprinted. The program will eventually track both the entry and departures of most non-immigrant visa holders.

Although US-VISIT will initially cover only about 25 million of the approximately 500 million people visiting the United States annually, the Department of Homeland Security calls it crucial to preventing new terrorist attacks.

Critics, including some members of Congress, are concerned the new procedures, when fully implemented by an October deadline, could produce delays and disruptions.

"We need to take great care with the way in which we implement the program, expand the program, and look at it in an ongoing basis, because the potential for damage to the economy is very serious," said David Plavin, who heads the Airports Council International, an organization devoted to increasing cooperation between airports in the United States and around the world.

The Department of Homeland Security says it is on track to meet the October 26 congressional deadline for implementing "US-VISIT" at all major ports of entry.

Maura Harty, assistant secretary of state for consular affairs, says some problems and delays are inevitable, even for travelers from "visa-waiver" countries.

"It's a relatively short-term problem to handle as the visa-waiver countries begin to come on board with their biometrically-enabled passport. But in the short-term we would see a serious impact on business travel, on academic institutions, on travel and tourism to this country," she said. "We will do our very best to facilitate the travel of those who are in an emergency situation, those who have time-sensitive travel, but there will be a serious impact on the visa-waiver countries and on our abilities to provide services to them in a short-term."

In his testimony Thursday, Mr. Hutchison said no final decision has been made yet with regard to how the US-VISIT program will be applied to 104 million Mexicans with "temporary border crossing cards."

One report Thursday by Associated Press suggested that the Bush administration is considering dropping the requirement for fingerprints and photographs for Mexicans intending short-term stays in the United States.