WASHINGTON — A massive database that the government will use to monitor every purchase made by every American citizen is a necessary tool in the war on terror, the Pentagon said Wednesday.

Edward Aldridge, undersecretary of Acquisitions and Technology, told reporters that the Pentagon is developing a prototype database to seek "patterns indicative of terrorist activity." Aldridge said the database would collect and use software to analyze consumer purchases in hopes of catching terrorists before it's too late.

"The bottom line is this is an important research project to determine the feasibility of using certain transactions and events to discover and respond to terrorists before they act," he said.

Aldridge said the database, which he called another "tool" in the war on terror, would look for telltale signs of suspicious consumer behavior.

Examples he cited were: sudden and large cash withdrawals, one-way air or rail travel, rental car transactions and purchases of firearms, chemicals or agents that could be used to produce biological or chemical weapons.

It would also combine consumer information with visa records, passports, arrest records or reports of suspicious activity given to law enforcement or intelligence services.

The Defense Advanced Research Projects Agency is home to the Pentagon's brightest thinkers -- the ones who built the Internet. DARPA will be in charge of trying to make the system work technically.

Rear Adm. John Poindexter, former national security adviser to President Reagan, is developing the database under the Total Information Awareness Program. Poindexter was convicted on five counts of misleading Congress and making false statements during the Iran-Contra investigation. Those convictions were later overturned, but critics note that his is a dubious resume for someone entrusted with so sensitive a task.

Aldridge said Poindexter will only "develop the tool, he will not be exercising the tool." He said Poindexter brought the database idea to the Pentagon and persuaded Aldridge and others to pursue it.

"John has a real passion for this project," Aldridge said.

TIAF's office logo is now one eye scanning the globe. The translation of the Latin motto: knowledge is power. Some say, possibly too much power. "What this is talking about is making us a nation of suspects and I am sorry, the United States citizens should not have to live in fear of their own government and that is exactly what this is going to turn out to be," said Chuck Pena, senior defense policy analyst at the Cato Institute.

Pena and others say the database is an even greater violation of privacy rights than Attorney General John Ashcroft's nixed proposal to turn postal workers and delivery men into government tipsters. No matter what protections Congress requires, Pena fears a database big enough and nimble enough to track the entire nation's spending habits is ripe for abuse.

"I don't think once you put something like this in place, you can ever create enough checks and balances and oversight," Pena said.

But proponents say big business already has access to most of this data, but don't do anything with it to fight terrorism.

"I find it somewhat counter intuitive that people are not concerned that telemarketers and insurance companies can acquire this data but feel tremendous trepidation if a government ventures into this arena. To me it just smacks of paranoia," said David Rivkin, an attorney for Baker & Hostetler LLP.

The database is not yet ready and Aldridge said it will not be available for several years. Fake consumer data will be used in development of the database, he said.

When it's ready, Aldridge said individual privacy rights will be protected. But he could not explain how the data would be accessed. In some cases, specific warrants would give law enforcement agencies access, he said. But in other cases the database might flag suspicious activity absent a specific request or warrant, and that suspicious activity could well be relayed to law enforcement or intelligence agencies.

"I don't know what the scope of this is going to be," Aldridge said. "We are in a war on terrorism. We are trying to find out if this technology can work."