WASHINGTON - For the past four years, without public notice, federal agents have assigned millions of Americans and other international travelers computer-generated scores assessing the risk they pose of being terrorists or criminals.

The travelers are not allowed to see or directly challenge these risk assessments. And the government intends to keep them on file for 40 years.

Earlier in November, the government disclosed the existence and details of the Automated Targeting System for the first time in the Federal Register. Privacy and civil liberties lawyers, congressional aides and even law enforcement officers said they thought the ATS had been applied only to cargo.

The scores are assigned to people entering and leaving the United States after computers assess their travel records, including where they are from, how they paid for tickets, their motor vehicle records, past one-way travel, seating preference and meals ordered.

The Homeland Security Department notice called it "one of the most advanced targeting systems in the world" and said U.S. ability to spot criminals and other security threats "would be critically impaired without access to this data."

Still, privacy advocates view ATS with alarm. "It's probably the most invasive system the government has yet deployed in terms of the number of people affected," David Sobel of the Electronic Frontier Foundation, a civil liberties group, said in an interview.

A similar DHS data-mining project for domestic air travelers caused a furor two years ago in Congress, which has barred its implementation until it can pass 10 tests for accuracy and privacy protection.