Homeland Security Secretary Michael Chertoff, who announced the changes, said they will help the United States boost the security of its visa-free travel program by allowing the government to screen visitors before they travel. Currently, visitors fill out paper forms en route and are screened by U.S. customs agents upon arrival.
The U.S. will begin implementing the changes in August, Chertoff said. Online registration will be mandatory for all visa-free travel by Jan. 12.
There are currently 27 countries whose citizens are not required to obtain visas for U.S. entry, including those in most of western Europe as well as Andorra, Australia, Brunei, Japan, New Zealand and Singapore. Eight other countries - among them the Czech Republic, Hungary and South Korea - are expected to be admitted to the visa waiver program.
When the Homeland Security Department began discussing the online registration rule last year, European businesses worried that business travel could be impeded.
But Chertoff argued that the system will simplify visa-free travel, because visitors will only be required to register online once every two years instead of filling out forms each time they travel.
The United Kingdom, whose citizens have long enjoyed visa-free travel to the United States, indicated it would accept the changes.
"Obviously we understand the need to improve travel security, and we welcome this additional information from the U.S. on when and where they are going to implement (the new measures)," a British Home Office spokeswoman said on the government's customary condition of anonymity.
The Confederation of British Industry, a business coalition, said it was reassured that the legislation contained provisions for last minute travel by business travelers.
Ahead of the announcement, European Union officials said they have been discussing the changes with Chertoff. Earlier this year, the EU unveiled plans for a similar travel authorization system for citizens from countries that have a visa-free regimen with the EU, but details have yet to be worked out.
"We have a clear visa reciprocity dialogue. This is something that needs to be kept in mind when this (U.S.) measure will be introduced," said Michele Cercone, a spokesman for EU Justice and Home Affairs Commissioner Jacques Barrot.
The visa-waiver program has been under fire by some U.S. lawmakers concerned that terrorists who are citizens of the participating countries can too easily obtain entry.
Chertoff said the new system will allow the United States to determine ahead of time if travelers pose a security risk. He called the system a "21st Century model for facilitating travel to the United States."
"It's very important to us to remain a welcoming country," he said, but added: "potential terrorists do not come easily labeled or identified."