The list kept by the National Counterterrorism Center (NCTC) -- created in 2004 to be the primary U.S. terrorism intelligence agency -- contains a far greater number of international terrorism suspects and associated names in a single government database than has previously been disclosed. Because the same person may appear under different spellings or aliases, the true number of people is estimated to be more than 200,000, according to NCTC officials.

U.S. citizens make up "only a very, very small fraction" of that number, said an administration official, who spoke on the condition of anonymity because of his agency's policies. "The vast majority are non-U.S. persons and do not live in the U.S.," he added. An NCTC official refused to say how many on the list -- put together from reports supplied by the CIA, the FBI, the National Security Agency (NSA) and other agencies -- are U.S. citizens.

The NSA is a key provider of information for the NCTC database, although officials refused to say how many names on the list are linked to the agency's controversial domestic eavesdropping effort. Under the program, the NSA has conducted wiretaps on an unknown number of U.S. citizens without warrants.

The government has been trying to streamline what counterterrorism officials say are more than 26 terrorism-related databases compiled by agencies throughout the intelligence and law enforcement communities. Names from the NCTC list are provided to the FBI's Terrorist Screening Center (TSC), which in turn provides names for watch lists maintained by the Transportation Security Administration and other agencies.

Civil liberties advocates and privacy experts said they were troubled by the size of the NCTC database, and they said it further heightens their concerns that such government terrorism lists include the names of large numbers of innocent people. Timothy Sparapani, legislative counsel for privacy rights at the American Civil Liberties Union, called the numbers "shocking but, unfortunately, not surprising."

"We have lists that are having baby lists at this point; they're spawning faster than rabbits," Sparapani said. "If we have over 300,000 known terrorists who want to do this country harm, we've got a much bigger problem than deciding which names go on which list. But I highly doubt that is the case."

Asked whether the names in the repository were collected through the NSA's domestic intelligence intercept program, the NCTC official said, "Our database includes names of known and suspected international terrorists provided by all intelligence community organizations, including NSA."

Attorney General Alberto R. Gonzales told the Senate Judiciary Committee last week that he could not discuss specifics but said: "Information is collected, information is retained and information disseminated in a way to protect the privacy interests of all Americans."

The NCTC name repository began under its predecessor agency in 2003 with 75,000 names, and it continues to grow. The center was created as part of a broad reorganization of U.S. intelligence agencies after the failure to disrupt the Sept. 11, 2001, attacks. It is the main agency for analyzing and integrating terrorism intelligence and is under direction of Director of National Intelligence John D. Negroponte.

Its central database is the hub of an elaborate network of terrorism-related databases throughout the federal bureaucracy. Terrorism-related names and other data are sent to the NCTC under standards set by Homeland Security Presidential Directive 6, signed by President Bush in September 2003, according to a senior NCTC official. The directive calls upon agencies to supply data only about people who are "known or appropriately suspected to be . . . engaged in conduct constituting, in preparation for, in aid of, or related to terrorism."

"We work on the basis that information reported to us has been collected in accordance with those guidelines," Vice Adm. John Scott Redd, the center's director, said in a statement.

Analysts at the NCTC review all incoming names and can reject them if they do not have an apparent link to international terrorists, officials said. "That is not common, but it does happen," an NCTC official said, citing as examples a domestic or foreign drug dealer or a member of a U.S.-based extremist group, when neither has any sign of international terrorist connections.

The NCTC then sends a subset of the repository list to the FBI's screening center, and each entry includes a reference "to how the individual is associated with international terrorism," according to a June 2005 report by Justice Department Inspector General Glenn A. Fine. This reference is assigned one of 25 codes such as "Member of a Foreign Terrorist Organization," "Hijacker" or "Has Engaged in Terrorism," according to the report. The report also notes that the codes are split in two categories: "Individuals who are considered armed and dangerous and those who are not."

Fine's office criticized the TSC for including nearly 32,000 records of people in the "armed and dangerous" category but giving them the lowest handling code, which means that no report needs to be sent back to the FBI if they are encountered in the United States by law enforcement officers.

The TSC consolidates NCTC data on individuals associated with foreign terrorism with the FBI's purely domestic terrorism data to create a unified, unclassified terrorist watch list. The TSC, in turn, provides, for official use only, a version giving each person's name, country, date of birth, photos and other data to the Transportation Security Agency for its no-fly list, the State Department for its visa program, the Department of Homeland Security for border crossings, and the National Crime Information Center for distribution to police.

Shannon Moran, a spokeswoman for the FBI screening center, declined to answer detailed questions about the center's work, including how many names are on its list, how many U.S. citizens are included and whether the FBI database includes names linked to the NSA program. Fine's office reported last year that the FBI database contained more than 270,000 names, including a large number of people associated with domestic terrorist movements such as radical environmentalists and neo-Nazi white supremacists.

"If being placed on a list means in practice that you will be denied a visa, barred entry, put on the no-fly list, targeted for pretextual prosecutions, etc., then the sweep of the list and the apparent absence of any way to clear oneself certainly raises problems," said David D. Cole, a Georgetown University law professor who has been sharply critical of the Bush administration's anti-terrorism policies.

The growth of terrorist-related data networks within the U.S. intelligence community has greatly accelerated since Sept. 11, 2001. Before the al Qaeda attacks on the World Trade Center and the Pentagon, there were databases containing terrorist identities at the CIA, Defense Intelligence Agency, FBI and State Department. In addition there were 13 independent watch lists, but the lists or databases were not interoperable.

Currently, according to an NCTC official, there are 26 classified data networks carrying terrorism material. In a December 2005 interview on Federal News Radio, Redd said his agency "is really the only place in government and certainly in the intelligence community where all counterterrorism intelligence comes together." He also said that analyses of terrorism issues from all 15 intelligence agencies come into the NCTC, which then puts them on its Web site.

"What that means," Redd said, "is about 5,000 analysts around the counterterrorist intelligence community can pull up that Web site and see . . . what every other agency has as well, assuming they have the clearances."

Marc Rotenberg, executive director of the Electronic Privacy Information Center, said the size of the NCTC list and other terrorism-related databases underscores the severity of the "false positive" problem, in which innocent people -- including members of Congress -- have been stopped for questioning or halted from flying because their names are wrongly included or are similar to suspects' names.

"One of the seemingly unsolvable problems is what do you do when someone is wrongly put on this watch list," Rotenberg said. "If there are that many people on the list, a lot of them probably shouldn't be there. But how are they ever going to get off?"