Federal officials are defending claims by civil liberties advocates that the government's watchlist of suspected terrorists, which critics say has topped a million names, is bloated and ineffective.

At a news conference on Monday, officers from the American Civil Liberties Union (ACLU) charged that the Bush administration has turned air travel into a "Kafkaesque" nightmare and urged systematic changes in the way the government compiles the names of individuals targeted for detention at airports and other points of entry.

The ACLU was joined by a former federal prosecutor and other travelers who have repeatedly been hassled by airport security solely because they share a name — often as common as "Jim Robinson" or "Gary Smith" — with an alias employed by a terrorist.

"The list is out of control," said Barry Steinhardt, director of the ACLU's Technology and Liberty Program on Government Data Mining. "There cannot possibly be one million terrorists threatening and poised to attack us. If there were, our cities would be in ruins...Perhaps tens of millions of Americans are caught up in a Kafkaesque web of suspicion."

But Chad Kolton, a spokesman for the Terrorist Screening Center (TSC), the multi-agency organization that maintains the watch list, told FOX News the ACLU that had confused the number of "records" on the watch list with the number of "individuals."

Only 400,000 or so individuals have been placed on the list, Kolton said, but many generate multiple "records" based on their use of aliases in job and credit applications and fake passports.

"It has been relatively easy to monitor the growth of the number of records in the system, because the database is expanding at a measurable pace," said Kolton.

Steinhardt admitted that the ACLU's number was an "extrapolation" based on figures provided in a report last year by federal investigators, and that the one millionth addition to the list might not take place until month's end or later.

In an April 2007 report, entitled "Follow-Up Audit of the Terrorist Screening Center," the Department of Justice's Office of Inspector General found the TSC's watch list consisted, at that time, of 700,000 "records," and was adding new ones at the rate of 20,000 per month. Among those on the list, the ACLU said, were nuns, members of Congress and war heroes.

Pressed on the multiple records point, Steinhardt held firm, saying: "No, this is one million actual names on the list."

Administered by the Federal Bureau of Investigation, the TSC was created by a Homeland Security Presidential Directive in September 2003. Its chief function was to integrate existing terrorist watchlists and help screen individuals who apply for visas, attempt to enter the U.S. through ports of entry, travel internationally on commercial airlines, or get stopped by a local law enforcement officer for suspected traffic violations.

Prior to the creation of the TSC, the federal government relied on at least a dozen separate terrorist watchlists maintained by different federal agencies.

The 2007 report by the Justice Department's internal auditor found that the TSC had "enhanced its efforts to ensure the quality of watchlist data" and increased the number of staff personnel assigned to data quality management. The report also found TSC had developed "a process and a separate office" to address complaints filed by individuals who claimed they were wrongly placed on the list.

However, the inspector general also identified "several known or suspected terrorists who were not watchlisted appropriately," and determined that while TSC was "following its procedures and reaching appropriate resolutions" in its reviews of citizens' complaints, such reviews "were not always completed in a timely manner."

FOX News' Ian McCaleb contributed to this report.