According to the investigative report by Pulitzer-prize winning journalist Ron Suskind, an informant close to al Qaeda management told U.S. officials that Ayman al-Zawahri canceled the plan in January 2003, despite the likelihood that the strike would have killed as many people as the Sept. 11 attacks.
CBS analyst Michael Scheuer said Zawahri probably called off the attack because it would not have been big enough. "They're not interested in an attack that is the same size as the last one," Scheuer said.
The informant said that operatives had planned to use a small, easily concealed delivery system to release hydrogen cyanide into multiple subway cars. U.S. officials had already discovered plans for the device in the computer of a Bahraini jihadist arrested in February 2003, and they had been able to construct a working model from the plans.
The easy-to-make device, called "the mubtakkar," meaning "invention" or "initiative," represented a breakthrough in weapons technology that "was the equivalent of splitting the atom," Suskind writes. All previous efforts to use the deadly gas, similar to that used in Holocaust-era gas chambers, in mass attacks had failed.
On CBS' Face The Nation, White House spokesman Tony Snow would not confirm or deny the reported plot.
"I don't want to confirm or deny this particular story," he told Bob Schieffer. "I just don't have anywhere to go with it."
The FBI declined to confirm the details of Suskind's account. Agency spokesman Bill Carter in Washington said Saturday that the bureau would have no comment on the excerpted material.
A New York Police Department spokesman said authorities had known of the planned attack. "We were aware of the plot and took appropriate precaution," Paul Browne said Saturday.
New York City Metropolitan Transportation Authority spokesman Tom Kelly declined comment.
According to the report, President Bush was shown a model of the weapon in March 2003 and ordered alerts sent through the U.S. government. When intelligence arrived that al-Zawahri had called off the attack, Mr. Bush worried that something worse was in the works, Suskind writes.
At least two of Suskind's sources remembered Mr. Bush saying, "This is bad enough. What does calling this off say about what else they're planning? ... What could be the bigger operation Zawahri didn't want to mess up?" the author said.
"What has been concluded for the most part is this: al Qaeda's thinking is that a second-wave attack should be more destructive and more disruptive than 9/11," Suskind told Time.
The book claims that al Qaeda's cyanide terror cell is still in the United States, reports CBS News correspondent Randall Pinkston. But, intelligence sources tell CBS News that, as far as they know, there are no terror cells operating in the U.S. under the command of Zawahri or bin Laden.
Sen. Charles Schumer of New York said on Sunday that revelations about the plot offer more proof that Department of Homeland Security officials were wrong when they decided to cut anti-terror funding for New York and other major cities.
"What this indicates is that the funding levels are just way off base," Schumer said. "When we know that New York is the number one targeted city by terrorists shows that something bad is at work."
The informant, who had become disgruntled with al Qaeda's leadership, linked the organization's top agent on the Arabian peninsula to the attacks, Suskind writes. The man was later killed in a violent standoff with Saudi authorities.
The excerpt of Suskind's forthcoming book, "The One Percent Doctrine," was to appear in Monday's print edition of Time. Suskind is a former reporter for The Wall Street Journal.