Al-Qaeda originally planned to crash as many as 10 hijacked aircraft in the US, a panel investigating the 11 September attacks has said.
The report says Bin Laden wanted to strike a year earlier
A preliminary report by the US national commission said the White House, the Capitol, CIA and FBI headquarters and sites in California were the targets.
It says Osama Bin Laden vetoed the plot in favour of attacks on the World Trade Center and the Pentagon.
Another report has found no "credible evidence" of Iraq's help to al-Qaeda.
The two preliminary reports were published before the final public session of the commission.
They contradict remarks by the US vice-president about Saddam Hussein's "long-established ties" with al-Qaeda.
Iraq's alleged links with al-Qaeda were part of the justification the Bush administration gave for invading Iraq.
The 11 September attacks killed nearly 3,000 people after members of Bin Laden's al-Qaeda network flew three hijacked planes into New York's WTC and the Pentagon, with a fourth crashing in Pennsylvania.
The commission, drawn from both Republicans and Democrats, published two separate preliminary reports: an Outline of the 9/11 Plot and an Overview of al-Qaeda.
The first report says top al-Qaeda suspect Khalid Sheikh Mohammed initially proposed a hijacking attack with 10 planes to hit an expanded list of targets, including unidentified nuclear plants and tall buildings in California and Washington state.
It says that Khalid Sheikh Mohammed - who has been in US custody for over a year - also wanted to take over an aircraft himself.
But - rather than crash it into a building - he planned to kill all the male passengers, release women and children and make a speech on US television denouncing Washington's policy in the Middle East.
The more ambitious plan was allegedly rejected by Bin Laden, who instead chose the WTC and the Pentagon.
The report says Bin Laden repeatedly called for the assaults to begin a year earlier, but the plot was only deferred because not enough trained pilots were available to fly aircraft into buildings.
It says some that some of the plotters had failed to complete their training or even learn adequate English.
The 11 September attacks planning was reportedly done in al-Qaeda camps in Afghanistan and may have cost al-Qaeda about $500,000.
The commission also found that al-Qaeda is still "extremely interested in conducting chemical, biological, radiological, or nuclear attacks".
On Thursday, top military and civilian aviation officials - including General Richard Myers, Chairman of the Joint Chiefs of Staff - will testify about their agencies' responses to the attacks.
A final report on the commission's findings is due on 28 July.
Bin Laden spurned
The other report - Overview of the Enemy - describes the roots of the militant network and its activities.
Bin Laden has not been sighted since 2001
It says Bin Laden had explored the possibility of co-operation with Iraq, despite his opposition to Saddam Hussein's secular regime.
A senior Iraqi intelligence officer had met Bin Laden in 1994 to hear his requests for space to establish training camps and assistance in procuring weapons - but Iraq had not responded.
"There have been reports that contacts between Iraq and al-Qaeda also occurred after Bin Laden had returned to Afghanistan, but they do not appear to have resulted in a collaborative relationship," the statement says.
"We have no credible evidence that Iraq and al-Qaeda co-operated on attacks against the United States."