Washington ? The independent commission investigating the 9-11 attacks released a strikingly detailed portrait of the Sept. 11 plot, describing how a group of Islamic radicals overcame internal discord and logistical setbacks to pull off the deadliest terrorist attack on America soil.

The report offered an inside look at the twists and turns of a conspiracy that originally envisioned an even more horrifying plan, calling for the hijackings of 10 planes, nine of which would strike targets on both U.S. coasts, including nuclear power plants and the headquarters of the CIA and FBI.

The alleged mastermind of the attacks, Khalid Sheikh Mohammed, planned to pilot the 10th plane himself, killing all the male passengers and then landing the plane and making a statement denouncing U.S. policy in the Middle East. Ultimately, he planned to release women and children passengers, according to a staff report of the panel.

Wednesday’s findings, contained in two interim reports, were released on the first day of the panel’s final two-day hearing. The panel also heard from a range of officials.

The commission’s final report, which is due in late July, is sure to play an important part in the election-year debate over the war in Iraq and the nation’s preparedness before the attacks on the World Trade Center and Pentagon.

Dissent among attackers

Among the most remarkable new details revealed by the commission was the sharp dissension among the plotters as their scheme came together. As late as Sept. 9, 2001, for example, the terrorists disagreed on whether the fourth plane — the one that ultimately crashed in Pennsylvania — should hit the White House or Capitol.

Al-Qaida leaders considered the Capitol “the perceived source of U.S. policy in support of Israel,” one interim report said, noting that Osama bin Laden considered the White House “a political symbol and wanted it attacked as well.”

In another striking detail, bin Laden’s top advisers wanted to call off the attack at the last moment, but he overruled them.

The commission’s report made it clear for the first time that that two of the plot’s top planners, Mohammed and Ramzi Binalshibh, both of whom are in U.S. custody, are speaking at length to interrogators. They were the apparent sources for many of the details reported Wednesday.

The two men are hardened Islamic Jihadists, and Mohammed was one of al-Qaida’s most senior leaders. The report shed no light on how the suspects were being questioned.

The commission staff was allowed access to written reports from U.S. intelligence operatives’ interrogation of more than 100 al-Qaida-linked detainees, but staffers were not allowed to meet personally with any of the prisoners.

Beyond the attacks themselves, the commission provided new details of al-Qaida’s reach and ambitions. The reports said al-Qaida training camps encouraged attendees to “think creatively about ways to commit mass murder.” Among the ideas that were hatched: forcing Russians to fire a nuclear missile at the U.S., mounting cyanide or mustard gas attacks on Jewish areas in Iran and injecting poison gas into the air system of a building.

In testimony before the commission, the FBI’s top counter-terrorism official, John Pistole, warned that even now authorities know “very little” about al-Qaida’s ability to launch another attack inside the U.S.

But the report said that the group “is actively striving to attack the United States and inflict mass casualties.”

Bigger plans

Mohammed has told interrogators that he originally conceived the 9-11 plot in 1999 as a more extensive attack that would include crashing hijacked planes into the tallest buildings in California and Washington state.

After bin Laden urged him to scale back the plan and two Yemeni potential pilots were determined unlikely to get U.S. visas, Mohammed revised the assault.

Still, he hoped to hijack U.S. airliners in Southeast Asia, where the Yemenis would be more likely to receive visas, and crash the planes. But, again, bin Laden urged him to scale back, arguing a simultaneous attack on another continent would be too difficult to coordinate with assaults on New York and Washington.

The hijackings were carried out with considerable advance planning. The first operatives entered the U.S. in January 2000. The four hijack pilots made “practice runs” during the summer of 2001 on coast-to-coast flights that employed the same aircraft models that would be hijacked a few months later.

All the hijackers flew first class on the practice runs. According to Binalshibh, the prospective pilots tested airport security by carrying box-cutters, the same type of weapons they later used to subdue passengers and cabin crews. They also determined that the best time to storm the cockpit would be 10 to 15 minutes after takeoff, when they noticed that cockpit doors were typically opened for the first time.

Planning problems

But, according to the staff reports, the preparations were far from smooth.

Two prospective pilots failed to make progress in their flight training and had to be replaced by better-educated operatives with a deeper knowledge of the West.

Mohammed intended to use larger teams to take over the