The terrorist attacks of Sept. 11, 2001, were originally envisioned as a more audacious assault involving 10 hijacked jetliners on the East and West coasts, but the plan was scaled back and later plagued by conflicts among al Qaeda's leaders and some of the hijackers themselves, according to a report issued by the panel investigating the assaults.

The date for the attacks was uncertain until about three weeks before they were carried out, and there is evidence that as late as Sept. 9, 2001, ringleader Mohamed Atta had not decided whether one aircraft would target the U.S. Capitol or the White House, the report by the Sept. 11 commission said.

Air Force Gen. Ralph E. Eberhart, commander of the North American Aerospace Defense Command, told the commission that U.S. fighter jets would have had enough time to shoot down all four commandeered jetliners if the Federal Aviation Administration had immediately notified military authorities about the planes' hijacking.

The commission report said an executive order by Vice President Cheney to shoot down hostile aircraft that morning did not come until long after the last hijacked airliner had crashed and was not passed on to fighter pilots in the air because of uncertainty about the order's ramifications.

The commission also reported that although contacts occurred, it had found no "collaborative relationship" between Iraq and al Qaeda, challenging one of the Bush administration's main justifications for the war in Iraq. The report said that Osama bin Laden "explored possible cooperation with Iraq" while he was in Sudan through 1996, but that "Iraq apparently never responded" to a bin Laden request for help in 1994.

Along with their contention that Saddam Hussein was stockpiling weapons of mass destruction, President Bush, Cheney and other top administration officials often asserted that there were extensive ties between Hussein's government and Osama bin Laden's terrorist network.

After the commission report was issued, Bush reasserted the existence of a relationship. "The reason I keep insisting that there was a relationship between Iraq and Saddam and al Qaeda: Because there was a relationship between Iraq and al Qaeda," Bush said.

Al Qaeda "is actively pooling whatever resources it has left at its disposal and, in a very centralized and methodical way, we believe that it is plotting an attack and moving an attack forward using what capabilities it has left to attack the homeland in the next few months," FBI counterterrorism chief John S. Pistole said.

-- Dan Eggen, Walter

Pincus and Dana Milbank

The Sept. 11 panel said that al Qaeda originally planned assaults involving 10 hijacked jets and that its investigation found no "collaborative relationship" between al Qaeda and Iraq.