WASHINGTON - As horrendous as they were, the attacks of Sept. 11, 2001, were only a small part of terrorist visions that foresaw using 10 hijacked airplanes to attack targets on both the East and West coasts, including the U.S. Capitol and the White House, the staff of the independent commission investigating Sept. 11 reported Wednesday.

Some of the Sept. 11 terrorist plans, the commission staff said, called for the hijacked jets to be crashed into the headquarters of the FBI and the CIA, various nuclear power plants, and skyscrapers in California and the state of Washington, a captured leader of al-Qaida, Khalid Shaikh Mohammed, has told interrogators.

Mohammed, who is believed to have originated the idea for the Sept. 11 attacks and whose nephew, Ramzi Yousef, was the mastermind of the 1993 bombing of the World Trade Center, was seized in Pakistan in March 2003 and is being held at an undisclosed location.

Wednesday's interim report on the outline of the Sept. 11 plot offers new details and far more context than has previously been known. It says, for instance, that Zacarias Moussaoui, who has often been dubbed "the 20th hijacker" out of speculation that he was to have joined the 19 actual hijackers, was instead meant to participate in a second wave of attacks, an idea thwarted when he was arrested in August 2001 after his behavior at a Minnesota flying school aroused suspicion. Moussaoui is awaiting trial on charges connected to the 9-11 plotting.

The Sept. 11 conspirators and their leaders, while joined in their hatred of the United States, often argued among themselves over what targets to attack, and when, the staff of the bipartisan investigating commission said.

"Given the catastrophic results of the 9-11 attacks, it is tempting to depict the plot as a set plan executed to near perfection," the report said. "This would be a mistake."

For instance, bin Laden, al-Qaida's top leader, initially pushed for a date of May 12, 2001, exactly seven months after terrorists attacked the American destroyer Cole in Yemen. Then, when he learned that Prime Minister Ariel Sharon of Israel would visit the White House in June or July, bin Laden pressed to amend the timetable.

"In both instances," the report states, Mohammed "insisted that the hijacker teams were not yet ready."

One apparent "failure" of the plot has been known since the day of the attacks: The Boeing 757 designated United Flight 93, which took off from Newark, N.J., crashed in a field in southwestern Pennsylvania, apparently after its hijackers struggled with the doomed passengers.

There has been conjecture ever since that the hijackers on Flight 93 meant to crash the plane into a high-profile Washington target - the White House, perhaps, or the Capitol. Another jet, hijacked after it took off from Dulles Airport, near Washington, crashed into the Pentagon, while two jetliners that were hijacked after taking off from Boston were flown into the World Trade Center, destroying the twin towers.

Khalid Shaikh Mohammed has told interrogators that "the U.S. Capitol was indeed on the preliminary target list" that he originally developed with bin Laden and other terrorist ringleaders as early as the spring of 1999.

"That preliminary list also included the White House, the Pentagon and the World Trade Center," said the staff of the commission, formally known as the National Commission on Terrorist Attacks Upon the United States. Mohammed "claims that while everyone agreed on the Capitol, he wanted to hit the World Trade Center, whereas bin Laden favored the Pentagon and the White House."

Among bin Laden and his confederates, the Capitol was "the perceived source of U.S. policy in support of Israel," while the White House was considered "a political symbol."

Bin Laden expressed his target preferences in the summer of 2001 to Atta, who was destined to fly a jetliner into the north tower of the World Trade Center. Had he not been able to hit the tower, Atta was determined to crash the jet he was flying into the streets of Manhattan, the report says.

In the weeks leading up to the attacks, the terrorists who were assigned to be "the muscle" in the hijackings, to stave off any resistance from passengers or crews, trained in gyms to prepare for their missions. The plotters had also studied airline schedules and had observed while on typical flights that cockpit doors were often open a quarter-hour or so after takeoff, - making that the best time for hijacking.