Washington and N.Y. Put on Alert

The operatives focused on structural features of the targets that might "prevent the buildings from toppling down," including the thickness of window glass. They discussed separate plans to hijack oil tankers but warned that some contain tracking devices, officials said.

Operatives also intensively monitored employees of the targeted buildings, noting the locations of employee offices in relation to parking garages and identifying local bars and restaurants where employees of the institutions could be met, officials said.

One senior U.S. official likened the new intelligence to a homeowner learning that someone had broken into his house years ago and had been monitoring the occupants all that time.

Such sophistication of planning is a hallmark of al Qaeda. At the U.S. embassy bombings trial in 2001, Jamal Amed al-Fadl, a former associate of Osama bin Laden's, testified that similar surveillance took place four years before the embassies in Kenya and Tanzania were bombed in 1998. Testimony showed that a team arrived in Nairobi in 1994, headed by Ali Mohammed, a former U.S. Army Green Beret now in prison, who had taught surveillance to al Qaeda recruits in Afghanistan training camps.

The team photographed buildings; analyzed access routes, building entrances and guard stations; and kept track of crowd flow around the embassy and other buildings in the area. Surveillance reports were sent to Afghanistan for review by bin Laden and Muhammad Atef, then his chief military planner. Atef, who made one visit to Kenya to review the scene, was killed in November 2001 during a U.S. bombing raid in Afghanistan.

An Aug. 6, 2001, presidential daily briefing obtained by the Sept. 11 commission included a warning about possible surveillance of federal buildings in Manhattan. The FBI has never located the Yemeni man who asked two other Yemenis to take photographs of the buildings.

A White House aide said Bush was informed of the potential threat Friday morning aboard Air Force One by his traveling CIA briefer, during a daily intelligence briefing. At that time, the CIA was still trying to cull the data, and Bush was told about "emerging information that might require us to take preventive action on certain specific targets," the aide said.

The CIA worked round-the-clock on the information for 72 hours before Ridge's announcement, officials said. Members of Bush's Cabinet met about the matter on Saturday and again at 10 a.m. yesterday for more than an hour.

Around noon, Bush authorized Ridge to make the announcement. White House officials said they wanted to make the announcement outside business hours so that workers in the buildings would not panic.

Just before Ridge went on television, Homeland Security officials offered Kerry a classified briefing detailing the intelligence, and the briefing was being scheduled yesterday afternoon, according to the Kerry campaign.

Kerry's senior adviser for national security, Susan Rice, said in a statement yesterday that the heightened alert indicates "we are not as safe as we could or should be" and underscores the need to implement the Sept. 11 panel's recommendations.

"John Kerry and John Edwards will bring all aspects of our nation's power to crush al Qaeda and destroy terrorist networks," Rice said.

Howard Dean, the former Vermont governor and Democratic presidential candidate, also questioned yesterday "how much of this is real and how much of this is politics." He said in an interview on CNN that "every time something happens that's not good for President Bush he plays his trump card, which is terrorism."

Other Democrats, including Sen. Joseph I. Lieberman (D-Conn.), said they did not doubt the credibility of the warning.

"I don't think anybody who has any fairness or is in their right mind would think the president or the secretary of homeland security would raise an alert level and scare people for political reasons," said Lieberman, who also sought the Democratic nomination for president. "That's outrageous."

Ridge said in a conference call with journalists that mayors and governors were notified before yesterday's announcement. He said teams of federal officials met with security officers at the targeted buildings yesterday afternoon.

Ridge indicated that other targets might be part of a al Qaeda plot, but that authorities are still working through the details. "There may be more to come," Ridge said. "We decided not to wait until we were done. We better get out with what we know now."

Staff writers Mike Allen, Juliet Eilperin and Spencer S. Hsu in Washington, and Michael Powell in New York, contributed to this report.