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 .
Government report : Three quarters of a million names on `` watch list '' Multiple names or aliases add to list 's complexity , GAO report says . ACLU urged Congress to tighten its oversight of the name compiling process .