ng to the Government Accountability Office report.

Hundreds of millions of people each year are screened against the lists by Customs and Border Protection, the State Department and state and local law enforcement agencies. The lists include names of people suspected of terrorism or of possibly having links to terrorist activity.

"Misidentifications can lead to delays, intensive questioning and searches, missed flights or denied entry at the border," the report said. "Whether appropriate relief is being afforded these individuals is still an open question."

When questions arose about tens of thousands of names between December 2003 and January 2006, the names were sent back to the agencies that put them on the lists, the GAO said. Half of those were found to be misidentified, the report found.

In December 2003, disparate agencies with counterterrorism responsibilities consolidated dozens of watch lists of known or suspected terrorists into the new Terrorist Screening Center run by the FBI.

People are considered "misidentified" if they are matched to the database and then, upon further examination, are found not to match. They are usually misidentified because they have the same name as someone in the database.

People are considered "mistakenly listed" if they were put on the list in error or if they should no longer be included on the list because of subsequent events, the report said.

Problems developed with terrorist watch lists after the terrorist attacks of Sept. 11, 2001.

Maher Arar, a Canadian software engineer, was detained at New York's Kennedy Airport in 2002 because Canadian officials had asked that he be placed on a watch list. The U.S. transferred him without court approval to Syria where he was tortured and imprisoned for a year. A Canadian inquiry found that Arar should not have been on the list because he didn't do anything wrong.

The no-fly list given to airlines to make sure terrorists don't board airplanes grew exponentially after the attacks on the World Trade Center and the Pentagon. The no-fly list is part of the Terrorist Screening Center database.

Young children and well-known Americans like Sen. Edward M. Kennedy, D-Mass., were stopped at airports because their names were the same as those on the no-fly list.

The list has contained the names of Bolivia's President Evo Morales and Nabih Berri, Lebanon's parliamentary speaker, according to a report by CBS'"60 Minutes," to be broadcast Sunday.

Richard Kopel, acting director of the screening center, said in a statement that Morales and Berri are not on the current no-fly list. He did not address whether they were in the past, noting only that the list changes daily.

Two international flights - in December 2004 and May 2005 - were diverted because passenger were misidentified as on the no-fly list.

Homeland Security Secretary Michael Chertoff said in a telephone interview with The Associated Press that watch lists aren't perfect.

"The watch list was the first stage of building a security net for the aviation system," Chertoff said.

He said an agreement reached Friday between the U.S. and the European Union would help prevent people from being misidentified.

The agreement calls for airlines to submit 34 pieces of data - including names, addresses and credit card details - about passengers flying from Europe to the United States.

The report said agencies are working to minimize the effect on people who are frequently misidentified.

TSA puts people on a special list of names that have been checked and cleared after they've complained to a call center and provided the agency more identification.

Customs annotates its database with a note that certain people shouldn't be stopped. As of September 2006, Customs annotated more than 10,300 names. Customs also gives preapproved low-risk travelers ID cards that provide expedited processing.

Customs acknowledged to the GAO that it needs to do a better job of providing guidance for their redress procedures for people who believe they've been misidentified.

The Justice Department is leading an effort to make sure that all agencies formally document opportunities for redress and that agency responsibilities are clear, the report said.