Since 1998, the FBI had observed "patterns of suspicious activity in this country consistent with preparations for hijackings or other types of attacks," according to a memo prepared for President Bush and declassified Saturday. They included evidence of buildings in New York possibly being cased by terrorists.
The document also said the CIA and FBI were investigating a call to the U.S. embassy in the United Arab Emirates in May "saying that a group of (Osama) bin Laden supporters was in the U.S. planning attacks with explosives."
A White House spokesman said the administration stands by its assertions that the memo contains no specific information that could have enabled the government to stop the attacks that took place on Sept. 11, according to CBS News Correspondent Mark Knoller.
The White House released the memo early in the evening on the Saturday before Easter, a time of very low news consumption.
Senior administration officials said Bush had requested the memo after seeing more than 40 mentions of al Qaeda in his daily intelligence updates during the first eight months of his presidency.
The Aug. 6, 2001, memo made plain that bin Laden had been scheming to strike the United States for at least six years. It warned of indications from a broad array of sources, spanning several years.
"Clandestine, foreign government, and media reports indicate bin Laden since 1997 has wanted to conduct terrorist attacks in the US," the memo to Bush stated. Bin Laden implied in U.S. television interviews in 1997 and 1998 that his followers would follow the example of World Trade Center bomber Ramzi Yousef and "bring the fighting to America."
The "presidential daily brief" said that after President Clinton launched missile strikes on his base in Afghanistan in 1998, "bin Laden told followers he wanted to retaliate in Washington."
The memo cited intelligence from another country, but the White House blacked out the name of the nation. It was the first time a presidential daily brief has ever been released publicly.
Efforts to launch an attack from Canada around the time of "Y2K" "may have been part of bin Laden's first serious attempt to implement a terrorist strike in the U.S.," the document states.
Convicted plotter Ahmed Ressam, who was caught trying to cross the Canadian border with explosives about 60 miles north of Seattle in late 1999, told the FBI that he alone conceived a planned attack on Los Angeles International Airport, but that bin Laden lieutenant Abu Zubaydah "encouraged him and helped facilitate the operation," the document said.
Al Qaeda members, some of them American citizens, had lived in or traveled to the United States for years, the memo said.
"The group apparently maintains a support structure that could aid attacks," it warned.
The document said that "some of the more sensational threat reporting" - such as warnings that bin Laden wanted to hijack aircraft to win the release of fellow extremists" - could not be corroborated.
One item in the memo referred to "recent surveillance of federal buildings in New York." A White House official speaking on condition of anonymity that that was a reference to two Yemeni men the FBI interviewed and concluded were simply tourists taking photographs.
On May 15, 2001, a caller to the U.S. embassy in the United Arab Emirates warned of planned bin Laden attacks with explosives in the United States, but did not say where or when.
The CIA reported the incident to other government officials the next day, and a dozen or more steps were taken by the CIA and other agencies "to run down" the information from the phone call, senior administration officials said Saturday evening.
One official said references to al Qaeda in prior presidential briefings "would indicate 'they are here, they are there' in other countries and the CIA director would tell the president what was being done to address "these different operations."
The official said those types of references prompted the president to ask for a report on domestic activity.
The senior administration officials refused to say what Bush's response to the memo was, or precisely what government action it had triggered.