Bush administration officials acknowledged yesterday that the latest terrorism alert was based primarily on information that is three to four years old, but they aggressively defended the decision to warn financial sectors in Washington, New York and Newark because of the continuing threat posed by al Qaeda.

Homeland Security Secretary Tom Ridge said at a news conference in New York that while much of the intelligence that led to the alert was dated, authorities were alarmed by evidence that al Qaeda computer files obtained last week had been updated as recently as January.

"I don't want anyone to disabuse themselves of the seriousness of this information simply because there are some reports that much of it is dated," Ridge said, adding: "When you see this kind of detailed planning, you have to take preemptive action."

Ridge's comments came after reports that the surveillance of five financial institutions in the three cities by al Qaeda operatives occurred as long as four years ago and that authorities were unsure whether it had continued since 2001. U.S. officials raised the terrorist threat level to orange -- or "high risk of terrorist attacks" -- on Sunday for financial services sectors in the three cities, suggesting initially that the plot was believed to be ongoing.

The debate over the surveillance information is the latest controversy over the administration's system of color-coded threat alerts, which have been criticized as vague and difficult for local officials and the public to act upon. The alert Ridge issued on Sunday, however, was narrowly targeted and based in large part on information that al Qaeda operatives had surveilled five buildings: the International Monetary Fund and World Bank headquarters in Washington; the New York Stock Exchange and Citigroup Center in New York; and the Prudential Financial building in Newark.

But authorities did not publicly make it clear until yesterday that the information compiled during that surveillance, contained on computer disks and documents seized during raids in Pakistan, was created in 2000 and 2001 or, in some cases, undated. Much of the information was also obtained from the Internet or other public sources, officials said.

Authorities issued somewhat conflicting signals yesterday about the timing of the surveillance. Frances Fragos Townsend, the White House deputy national security adviser for terrorism, said in a television interview that "the casings were done in 2000 and 2001." Ridge said the information "might be two or three years old," adding that "there's no evidence of recent surveillance."

White House press secretary Scott McClellan, meanwhile, told reporters that "it's wrong and plain irresponsible to suggest that [the alert] was based on old information."

Two senior intelligence officials stressed yesterday that the U.S. government has information from interrogations of recently captured al Qaeda operatives and other seized documents that buttresses the assertion that U.S. financial sites, possibly including the five buildings, were targeted for attack.

The pre-Sept. 11 computer files "are corroborated by other intelligence of strong credibility that is of a very, very current nature," one of the officials said, referring to intelligence from detainee interrogations and other documents.

One said the government has "very, very recent information showing a clear terrorist intent related to planning attacks," and said the computer files related to the casings are "part of a larger package of information we gained access to." Taken together, the information makes clear that "this is not information for information's sake," one of the officials said. "The context is attacking."

The two senior officials defended their explanation of the orange alert Sunday, saying it referred to the computer files from 2000 and 2001 and to several more current streams of intelligence.

"We were doing what we thought was our job, to uphold our sworn duty to protect people, and now we're being criticized for doing it," one official added. "The detail and specificity of the [computer] reports was so striking and dramatic that we felt we had no choice" but to consider releasing it.

Law enforcement officials, who declined to be identified because classified information is involved, said the earliest entry in the surveillance documents found on the computer was January 2000. U.S. officials are attempting to determine the age of some recovered paper documents.

The law enforcement officials and others said one of the computer files, which was related to one of the five buildings put on alert, was opened as recently as this January. The CIA and other intelligence agencies are still working to determine whether the file was changed in any way. The file contained photographs of the building in question, a law enforcement official said.

In all, the materials include about 500 photographs, drawings and diagrams, officials said.

The ramp-up to Sunday's alert began three days earlier, when acting CIA Director John E. McLaughlin presided over the CIA's daily 5 p.m. counterterrorism meeting. Attended by representatives of every major intelligence agency, such as the FBI, the National Security Agency and the Pentagon, the meeting included extensive discussions of the newly acquired material.

Intelligence officials would later describe it as the most remarkable "treasure trove" of information about an al Qaeda plot that many of them had ever seen. Officials said the documents showed meticulous and long-running surveillance of the targets, including counts of pedestrian traffic, details about employee routines and discussion about the kinds of explosives that might work best to destroy each building.

President Bush was informed Friday morning aboard Air Force One, during his daily intelligence briefing, an aide said. The CIA, which worked around the clock for the next 72 hours translating and attempting to make sense of the material, told Bush about "emerging information that might require us to take preventive action on certain specific targets," the aide said.

Paul Brown, deputy commissioner for public affairs at the New York Police Department, said Commissioner Ray Kelly learned about the emerging information late Friday. Brown said the details were alarming.

"It doesn't take a genius to know that bin Laden would like to hit Wall Street," Brown said, referring to Osama bin Laden, leader of the al Qaeda network. "Now we go to last Friday. We hear very good reconnaissance, and we put it together with what we know and our past experience, and I'd say that our response was rational from our point of view."

The plans for what to release publicly were made during a 90-minute meeting that began at 10 a.m. Sunday in the White House situation room, with some officials calling in over secure phone lines. Bush authorized raising the alert after church services that morning, aides said.

The public alert was preceded by an unusual conference call between Ridge and news executives at 1 p.m. Sunday, in which he talked about "a most unusual set of circumstances where, from a variety of different sources that we continue to exploit, there's a convergence of information that compels us to talk publicly about specific potential targets."

Bush and his top aides said yesterday that they knew much of the information that inspired the terrorist alert was years old but reacted urgently because they saw echoes of the long planning that preceded the Sept. 11 attacks, administration officials said yesterday.

"The fact that the casing began over the course of a longer period of time is consistent with how al Qaeda operates but does not suggest that the information itself was not then outdated or not relevant," White House communications director Dan Bartlett said.

But Ivo H. Daalder, a senior fellow at the Brookings Institution who was a National Security Council official under President Bill Clinton, said it "would have been useful for Mr. Ridge to have explained that information they were acting on was largely old."

"I don't doubt that this information was found -- I don't think they made it up," Daalder said. "But there is a real question of: Are we finding the kind of information that ought to worry and concern us as much as it has at the moment?"

Ridge dismissed such criticism yesterday. "I wish I could give them all top-secret clearances and let them review the information that some of us have the responsibility to review," he said. "We don't do politics in the Department of Homeland Security."

Staff writers Mike Allen, Spencer S. Hsu, Del Quentin Wilber, Dana Priest and Walter Pincus in Washington and Michael Powell in New York contributed to this report.

A police officer stands guard with an automatic weapon outside the New York Stock Exchange, one of the buildings that al Qaeda has surveilled.