The terrorist attacks of Sept. 11, 2001, were originally envisioned as an even 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 yesterday by the panel investigating the attacks.

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 ringleader Mohamed Atta had not decided whether one aircraft would target the U.S. Capitol or the White House, according to the report. Atta finally chose a date after the first week of September, the report says, "so that the United States Congress would be in session."

The 20-page document represents the most vivid, detailed and authoritative account of the plot to emerge since the 19 hijackers killed nearly 3,000 people by crashing four jetliners into the World Trade Center, the Pentagon and the Pennsylvania countryside. The document, brimming with new details, features a revealing examination of the thinking and actions of al Qaeda leaders, including Osama bin Laden, and demonstrates how relentlessly the terrorists pursued the plan to its deadly ends.

It also provides the most extensive view so far of what has been learned from secret interrogations of al Qaeda operatives now in U.S. custody, particularly Khalid Sheik Mohammed, mastermind of the attacks, and Ramzi Binalshibh, the would-be hijacker who could not gain entry to the United States and became the coordinator of the plot from Germany.

The narrative portrays bin Laden as a micromanager deeply involved in planning the strikes. He chose all 19 hijackers himself and constantly pushed to move up the attacks, seeking to carry them out as early as the middle of 2000.

Mohammed, the document shows, was the overeager lieutenant who first proposed using airplanes as missiles, but whose grandiose plans were curtailed several times in the face of logistical obstacles. The entire plot, from start to finish, cost al Qaeda only $400,000 to $500,000, the investigation found.

At the same time, the report reveals serious rifts among the hijackers and within the upper ranks of al Qaeda. One of the pilots crucial to the hijack plan, Ziad Samir Jarrah, nearly abandoned the plot and probably would have been replaced by alleged conspirator Zacarias Moussaoui, the only person in the United States charged in connection with the attacks, the report concludes.

But bin Laden's fervor persisted despite opposition from some of his closest aides, who urged him to abandon the plan as it neared completion in the summer of 2001.

Bin Laden believed "that an attack against the United States would reap al Qaeda a recruiting and fundraising bonanza," the report concludes. "In his thinking, the more al Qaeda did, the more support it would gain. Although he faced opposition from many of his most senior advisers . . . bin Laden effectively overruled their objections, and the attacks went forward."

The findings were contained in one of two reports issued yesterday as part of the last round of public hearings held by the National Commission on Terrorist Attacks Upon the United States. The panel, which is to issue a set of conclusions on the nation's air defense system today, is scheduled to complete its wide-ranging final report by next month.

Commission members and witnesses also warned yesterday of the continuing danger posed by al Qaeda, despite the United States' aggressive campaign to thwart it. FBI counterterrorism chief John S. Pistole said that counterterrorism officials have "probably prevented a few aviation attacks" in the United States but that some of the operatives in those plots remain at large.

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," Pistole said.

In their account of the Sept. 11 plot, the panel's staff investigators generally concur with the FBI that there is little evidence that knowing accomplices in the United States aided the plot. The report rules out terrorist connections to a Saudi national who helped two of the hijackers find an apartment in San Diego and found no evidence that the Saudi royal family or government funded the plot. A previous investigation by a joint House-Senate inquiry raised questions about possible complicity by other Saudis besides the 15 hijackers from the desert kingdom.

But the commission raises new questions about a handful of other individuals connected to the hijacking teams, including a man recently deported to Yemen who allegedly bragged to a cellmate about helping two of the hijackers.

The panel identifies 10 candidates besides Binalshibh who were considered for inclusion in the attacks but backed out or were removed by al Qaeda leaders. One was a Tunisian named Abderraouf Jdey, who may have been part of the Sept. 11 plot or a later attack and is now the subject of a global FBI manhunt.

Al Qaeda originally envisioned 25 to 26 hijackers taking part, as many as seven hijackers on each plane, Mohammed said. One investigator said that even late in the game, Mohammed would have tried to arrange the hijacking of as many as six jetliners if he had recruited enough pilots.

As the plot evolved, however, so did the participants and the potential targets, according to the report. Bin Laden approved and then abandoned a plan for simultaneous jetliner hijackings in the United States and Southeast Asia, and he and Mohammed would later curtail the plan again, eliminating the West Coast component. Bin Laden also discarded Mohammed's wish to personally commandeer one aircraft and use it as a platform to denounce U.S. policies on the Middle East.

"The centerpiece of his original proposal was the tenth plane, which [Mohammed] would have piloted himself," the report notes. Instead of crashing it in a suicide attack, Mohammed would have killed every adult male passenger on the plane, contacted the media while airborne and landed at a U.S. airport. There he wanted to deliver his speech before releasing all the women and children, the report says.

Planning for the assaults began in earnest in 1999. The targets considered over the next two years included not only those hit on Sept. 11, but also the headquarters of the CIA and the FBI; nuclear power plants; and the "tallest buildings in California and Washington State," according to the report. Bin Laden was intent on striking the White House, while Atta and Mohammed argued that the Capitol was an easier target.

Atta told Binalshibh he would try to hit the White House but reserved the option to have Jarrah divert toward the Capitol if that proved impossible. As late as Sept. 9, 2001, the report indicates, the fourth target may still have remained uncertain.

The evidence is mixed on whether al Qaeda had a practical plan for a "second wave" of attacks, the report shows. Mohammed told his interrogators that Moussaoui was part of such a plan, which also included Jdey and another operative named Zaini Zakaria. But the latter two had backed out by the summer of 2001, according to the report, and Mohammed said that by that time "he was too busy with the 9/11 plot to plan the second wave attacks."

The investigators indicate that plan was beset by garden-variety organizational problems and personality conflicts, concluding that "internal disagreement among the 9/11 plotters may have posed the greatest potential vulnerability for the plot." Khalid Almihdhar and Nawaf Alhazmi, the plot's first volunteers, were unable to complete either English language or pilot training after entering the United States in January 2000. Mohammed would have removed them altogether if bin Laden had not favored them, the report says.

But perhaps the most serious conflict is the one that developed between Atta -- the plot's "emir," or leader -- and Jarrah, a trained pilot who would help commandeer Flight 93, which crashed in Pennsylvania. In a coded message, Mohammed referred to the two as an unhappy couple on the cusp of divorce.

Jarrah was more gregarious and seemingly westernized than his accomplices, and he pined for his girlfriend. He had married her in an Islamic ceremony not recognized by German law, and called her almost daily. The breaking point appears to have come in July 2001, when Atta took Jarrah to the Miami airport for a one-way flight to Germany.

Although Jarrah would rejoin the plot the next month after an "emotional conversation" with Binalshibh, the panel concludes that there is significant evidence that Mohammed was preparing Moussaoui to take Jarrah's place.

The panel also portrays an ongoing high-level argument among bin Laden, Mohammed, Atta and others over the timing of the attacks. Bin Laden, the report says, "had been pressuring [Mohammed] for months to advance the attack date," asking that the attacks occur as early as mid-2000 after Ariel Sharon, then an Israeli cabinet minister, visited a Jerusalem site sacred to both Muslims and Jews. In 2001, Mohammed said, bin Laden pushed for a May 12 attack date -- exactly seven months after the bombing of the USS Cole in Yemen -- and later for June or July, to coincide with a visit by Sharon to the White House.

"In both instances," the report says, Mohammed "insisted that the hijacker teams were not yet ready. Other al Qaeda detainees also confirm that the 9/11 attacks were delayed during the summer of 2001, despite bin Laden's wishes."

Israeli Embassy spokesman Mark Regev said: "This is the first I've heard of any targeting of Sharon. I do know that on 9/11 our embassy was evacuated, a very rare move. Obviously, there was a perception that the embassy was a possible target."

Bin Laden also had to wrestle with demands by Taliban leader Mullah Omar, who provided al Qaeda sanctuary in Afghanistan, to avoid direct attacks on the United States. Many of bin Laden's own advisers sided with Omar and urged him to call off the plot, the report shows.

The document also mentions a long controversial intelligence tip received by the CIA in June 2001 that Mohammed was sending operatives to the United States for a mission. Democratic commission member Timothy J. Roemer, a former Indiana congressman, sharply questioned FBI and CIA officials yesterday about that information, demanding to know why it did not prompt more investigation.

The report notes that Mohammed "was widely known within al Qaeda to be planning some kind of operation against the United States." In the companion report also released yesterday, investigators say that bin Laden was intent on carrying out attacks on the United States as early as 1992, but U.S. officials were not aware of the plans or knowledgeable about his organization until four years later.

As al Qaeda developed, its terrorist training camps in Afghanistan provided fertile ground for its operatives "to think creatively about ways to commit mass murder," the investigators said. The ideas included "taking over a launcher and forcing Russian scientists to fire a nuclear missile at the United States; mounting mustard gas or cyanide attacks against Jewish areas in Iran; dispensing poison gas into the air conditioning system of a targeted building; and last, but not least, hijacking an aircraft and crashing it into an airport terminal or nearby city."

Staff writers Susan Schmidt and William Branigin contributed to this report.

Al Felzenberg, spokesman for the Sept. 11 commission, confers with Chairman Thomas H. Kean, left, and Vice Chairman Lee H. Hamilton, right. The panel, which is to issue its findings on the nation's air defense system today, is to finish its final report by next month.Commissioner Bob Kerrey listens to a presentation on the plot that resulted in the Sept. 11, 2001, attacks as a photograph of Khalid Sheik Mohammed, the mastermind of the attacks, is shown. Ramzi Binalshibh was a would-be hijacker who helped coordinate the attacks from Germany after being denied entry to the United States.As late as Sept. 9, 2001, Mohamed Atta -- shown in a bank video -- had not decided whether one plane would target the Capitol or the White House.