WASHINGTON – The recent disclosure that a Pentagon unit experimenting with data-mining technologies apparently linked the ringleader of the September 11, 2001, attacks to a Brooklyn-based terror cell more than a year before the strikes is prompting new questions about whether the Pentagon and Congress acted too hastily when they publicly disavowed such database intensive research in 2003.

Leading the crusade for greater use of the data-mining technique, sometimes called pattern analysis or link analysis, is Rep. Curt Weldon, a Republican of Pennsylvania. “The capability of doing massive data mining using massive supercomputers like Crays is, in my opinion, the overriding tool in the war against terrorism,” Mr. Weldon said in an interview with The New York Sun yesterday. “We don’t have the capability. We need it.”

Mr. Weldon, 58, has been preoccupied with the issue for years. In that time, his blunt and persistent approach has managed to irritate, if not anger, much of the intelligence establishment. Now, however, the 10-term congressman has stumbled onto what may be the most powerful piece of anecdotal evidence ever produced in favor of the technology, which involves using high-powered computers to sift through enormous quantities of data from a host of public and private sources.

The startling suggestion that a Defense Department unit was on the trail of Mohammed Atta and other terrorists more than a year before they struck was aired by Mr. Weldon for the first time on the House floor on June 27, 2005. The congressman delivered the so-called special order speech just before midnight, during a period reserved for lengthy remarks that are almost always ignored by the press.

“Mr. Speaker, for the first time I can tell our colleagues that one of our agencies not only identified the New York cell of Mohammed Atta and two of the terrorists, but actually made a recommendation to bring the FBI in to take out that cell,” Mr. Weldon said in his remarks.

The unit that fingered Atta and connected him to a suspected Al Qaeda terror cell in Brooklyn was code-named, “Able Danger,” according to the congressman and officials at the Pentagon. “Able Danger” involved staff from the Army’s Information Dominance Center who operated under instruction from the Special Operations Command.

At some point in mid-2000, while the unit was running data-mining experiments, the computer produced Mohammed Atta’s name along with a suggestion he was linked to other suspected Al Qaeda operatives. “Those connections led back to a Brooklyn cell, and that Brooklyn cell contained four of the terrorists,” Mr. Weldon said yesterday.

While the “Able Danger” project was little discussed until recently, a broader Pentagon data-mining effort, known originally by the Orwellian name, “Total Information Awareness,” was shuttered in 2003 after an outcry from privacy advocates. Some who were critics of that program say the recent developments suggest that the data-intensive technologies now deserve a second look.

“We did dismiss it too quickly,” said Sonia Arrison, the director of technology studies at a San Francisco think tank, the Pacific Research Institute. “I was really against TIA when it first came out,” she said.

Ms. Arrison said it makes little sense to demand that the government abandon a technology that is being used more and more widely by retailers and others in the private sector. She said the government should move forward with the program but eschew the secrecy that usually surrounds such efforts. “Let’s embrace a TIA-type system, but let’s have everyone understand how it works,” the analyst said. “The technology is really just a tool. It can be used for good or evil. … You can’t put it back in the bottle.”

Ms. Arrison said researchers at Pepperdine University are using the technology to seek patterns that could identify corrupt government officials.

Mr. Weldon said the Total Information Awareness program was hamstrung by several factors, including the association of its director, Admiral John Poindexter, with the Iran-Contra scandal. “We put the wrong person in and put the wrong spin on it,” the congressman said. “Somehow, it became a massive, ‘Big Brother’ spying effort on the American people. That perception killed what was a necessary effort.”

Efforts to reach Mr. Poindexter for this story were not successful.

While the Congress eliminated funding for the Total Information Awareness program in 2003, experts in the field assert that some data mining efforts have continued in classified programs that have no public budget.

According Mr. Weldon, the “Able Danger” team proposed providing the data on Atta to the FBI, but it was stopped by Defense Department lawyers who feared running afoul of guidelines and legal restrictions that govern intelligence agencies and the military.

The basis for the attorneys’ decision, which Mr. Weldon said he heard about from one of the “Able Danger” officers, is not clear. In general, a 1981 executive order bars intelligence agencies from disseminating information about American citizens and legal permanent residents of this country. However, Atta and the other hijackers did not fit that definition and, in any event, exceptions to the order allow sharing of some terrorism-related information.

Mr. Weldon is currently engaged in a public tussle with the members and staff of the so-called September 11 Commission over why that body omitted all discussion of the “Able Danger” project from its report. Commission members initially said they were unaware of the claims that the project had fingered Atta. However, they have since conceded that members of the commission’s staff were briefed on the claim in July 2004, just before the panel released its report.

A spokesman for the commission, Al Felzenberg, did not return calls yesterday seeking comment for this story, but according to news reports, the commission staffers disregarded the information about Atta because he arrived in America in June 2000 and could not have been in Brooklyn in 1999 or early 2000, as the military computer team suggested.

Mr. Weldon said yesterday that was a specious reason for failing to thoroughly explore the “Able Danger” data and not acting upon it. “It wasn’t about timelines. It was about linkages,” he said. “That’s nothing but B.S. and nothing but spin. They’re trying to spin their way out.”

Most privacy advocates appear to be unmoved by the news that data mining could have helped the government find the September 11 hijackers in advance.

“It actually does not cause us to rethink this,” a legislative counsel for the American Civil Liberties Union, Timothy Sparapani, said. “The American public’s most sensitive personally identifiable information should not be subjected to this kind of experiment unless and until we have some kind of confidence that society is going to get some kind of tangible benefit out of it.”

However, Mr. Sparapani said the failure to act on the information that was developed does merit investigation. “The problem is nobody conveyed it to anyone who could do anything about it. It says to me enormous structural divisions in the intelligence community need to be overcome,” he said.

An attorney with the Electronic Frontier Foundation, Kurt Opsahl, said the government should not be allowed to collect personal data on Americans, even if it might prevent an act of terrorism. “It is essential that people be able to maintain their privacy and their day-to-day transactions are not placed under government scrutiny,” he said.

Mr. Weldon said he favors safeguards that would prevent any surveillance system from generating data about American citizens. Over the administration’s objections, the House passed legislation last month that would require an annual government-wide report on data-mining projects.