Harriet Chiang, Chronicle Legal Affairs Writer

Conspiracy theorists, anti-war activists and those with healthy doses of skepticism about the official version of the Sept. 11 terrorist attacks converged in San Francisco on Friday for a three-day conference to try to figure out what really happened in the worst act of terrorism on American soil.

The gathering includes a hodgepodge of writers, filmmakers, and activists peddling their own version of what they claim was a cover-up by the Bush administration. In essence, they believe the administration knew about the attacks ahead of time but failed to act so that they could go to war against Afghanistan and Iraq.

The administration "motivated America into a war to control the last of the world's oil reserves,'' said Michael Ruppert, a former Los Angeles police officer who has a Web site devoted to what he believes really happened before the attacks.

The conference comes at a time when the public is focused on events surrounding the attacks. In dramatic testimony this week in Washington, D.C., before an independent commission investigating the attacks, former White House official Richard Clarke criticized the Bush administration for not taking al Qaeda threats seriously prior to the attacks and then, afterward, for wasting valuable resources on Iraq that could have been used to fight terrorism.

At this weekend's event at Herbst Theatre, skeptics of the official version of the terrorist attacks -- that the Bush administration didn't have any advance warning and couldn't have prevented the attacks -- are hashing out what they believe happened and who was responsible.

"We don't know precisely what happened,'' said Carol Brouillet, a Palo Alto activist who is organizing the event, International Inquiry into 9/11. "We're trying to provide a safe place for witnesses to come forward.''

"There is a 9/11 truth movement,'' said Nicholas Levis, another event organizer, as he addressed reporters while standing in front of a sign that read "Stop the 9/11 Cover-Up." Accusing the Bush administration of stonewalling,' he echoed the sentiments of other speakers that the White House had known ahead of time of the terrorist attacks, using it as an excuse to go to war in Afghanistan and Iraq.

In piecing together strands of evidence, he noted that The Chronicle had reported the day after the attacks that Mayor Willie Brown had been planning to fly to New York on Sept. 11 for a mayors' conference but had received a call the day before from someone in security at San Francisco International Airport advising him that Americans should be careful about air travel.

Brown refused to identify the source of the warning, saying it came from "my security people at the airport.'' Levis said the people attending the conference wanted to know where the warning had come from.

During the conference, participants also are ruminating over theories that the CIA created al Qaeda, that the military saw the planes heading for their targets but chose not to shoot them down and that there were links between Osama bin Laden and high level officials of the Bush administration.

Although organizers have no power to subpoena official documents, they have plenty of material to take offer for consideration. Participants will view a showing of the documentary "Aftermath - Unanswered Questions from 9/11'' as well as other films outlining the events that led to the fateful day.

The speakers include Ellen Mariani, whose husband, Louis, was a passenger on the plane that slammed into the South Tower of the World Trade Center. She has sued President Bush and members of his administration for negligence and has stated publicly she does not trust the commission in Washington to uncover the truth.

As she faced a roomful of reporters and activists Friday, Mariani recalled how her husband was on his way to their daughter's wedding, having taken a flight two hours after hers left, when it crashed. "I had to give her away,'' she recalled as she choked back tears.

"I waited 2 1/2 years for justice, and it never came,'' Mariani said. She accused the government of lying to her and discouraging her from asking questions. "The more I wait,'' she said, "the more determined I get.''

A "dialogue room'' will be available during the conference for those who want to talk to the speakers one-on-one and meeting rooms for those who want to get together in small groups.

Meanwhile, Ken Lisaius, a White House spokesman, said he refused to dignify the organizers' charges of a cover-up with a response.

He said the administration had fully cooperated with the commission, furnishing more than 2.3 million pages of documents and holding more than 100 briefings.

"The president has directed his administration to support efforts to insure an attack like this will never happen to this country again,'' he said. "That's why it's provided unprecedented access to information and documents.''

E-mail Harriet Chiang at hchiang@sfchronicle.com.