WASHINGTON (CNN) -- A new government report says there are now more than three quarters of a million names on the U.S. government's terrorist "watch list," raising concerns the list may be becoming too large.
Sen. Joe Lieberman, chairman of the Senate Homeland Security Committee, is concerned about the list's size.
A Government Accountability Office study out Wednesday said the Terrorist Screening Center's watch list contained approximately 755,000 names. But because many potential suspects have multiple names or aliases on the list, investigators are not certain how many distinct individuals are actually represented.
Officials at the Terrorist Screening Center told CNN in September that the number of individuals on the list is about 300,000.
Sen. Joe Lieberman, the chairman of the Senate Homeland Security Committee, said the "sheer size" of the list raises concerns. Lieberman, I-Connecticut, said the list contains an even higher number of records than 755,000.
"It contained 158,000 names including aliases in July 2004," Lieberman said during a hearing on the list. "That grew to 755,000 names by May of this year, and now stands at about 860,000 names just five months later. That's nearly a 500 percent increase in three years."
Timothy Sparapani, a lawyer for the American Civil Liberties Union, urged Congress to tighten its oversight of the process "before we all become suspects in the eyes of the Terrorist Screening Center."
Overall, the GAO -- the investigative arm of Congress -- credited the Terrorist Screening Center, which compiles the government's unified watch list, for making improvements in the system and providing a reliable single coordination point for terrorist screening data.
But found the government "has not finalized guidelines for using watch list records within (key segments of) the private sector."
The GAO report said government agencies had encountered individuals who were on the watch list about 53,000 times since the system was started in December 2003. That number includes repeat matches from the same individuals multiple times.
Most of the hits did not result in arrests because of a lack of sufficient evidence of any terrorist or criminal activity. But Deputy Assistant Homeland Security Secretary Paul Rosensweig said that is only part of the picture.
"With our current security layers,we have prevented thousands of dangerous people from entering the United States, including individuals suspected of terrorism, murderers, rapists, drug smugglers and human traffickers," Rosensweig said. "In fiscal year 2007, Customs and Border Patrol alone encountered 5,953 positive watch list matches."
Wednesday's report comes on the heels of a Justice Department inspector-general's report, which expressed concern about the quality of some of the data in the watch list, but noted continuing improvement in the system.
Terrorist Screening Center Director Leonard Boyle expressed particular satisfaction with the recent execution of a multi-agency agreement, which he said "provides a full and fair review of any watch list record that is the cause of an individual's complaint."
Lieberman and Sen. Susan Collins, R-Maine, said they were concerned about a report that a Mexican citizen with tuberculosis was able to cross the border into the U.S. more than 20 times without being stopped.
Rosensweig attributed the problem to a complicated and unusual pattern in the man's name combined with inaccurate birth date information. E-mail to a friend