Alexandria, Va. ? Zacarias Moussaoui pleaded guilty Friday to conspiring with the leaders of the Sept. 11, 2001, attacks to kill Americans and said he was chosen by Osama bin Laden to strike the White House.

Moussaoui, a 36-year-old French citizen of Moroccan descent, calmly told U.S. District Court Judge Leonie Brinkema that he understood he could face execution by admitting guilt on all six counts of conspiracy to commit acts of terrorism and air piracy.

“I can’t expect any leniency from the Americans,” he said. He added later: “Moussaoui will fight every inch against the death penalty.”

Atty. Gen. Alberto Gonzales, at a news conference after the court hearing, affirmed that the Justice Department will seek the death penalty against the only person in the United States ever charged in connection with the terror attacks on the World Trade Center and Pentagon, which killed almost 3,000 people.

“The fact that Moussaoui participated in this terrorist plot is no longer in doubt,” said Gonzales, who noted that prosecutors made no plea agreement with the defendant.

Prosecutors wouldn’t say exactly what Moussaoui’s role on 9-11 would have been if he hadn’t been arrested while at a flight school in Minnesota on immigration charges the month before the attack.

But as part of his guilty plea, Moussaoui signed a five-page statement of facts that Gonzales called “a chilling admission of guilt.” In it, Moussaoui said he lied after his arrest to “allow his ‘brothers’ to go forward” with the attacks.

The bearded Moussaoui, unshackled and wearing a green jumpsuit, read the document silently for a full five minutes before signing it. He never explained why he decided to plead guilty after more than three years of pretrial court battles.

His lawyers argued that he wasn’t competent to make that decision, but Brinkema said she decided at a closed hearing Wednesday that he was “completely capable” of entering a guilty plea against his lawyers’ advice.

In a rambling explanation Friday, Moussaoui talked about his role in an al-Qaida plot that he said was separate from the Sept. 11 attacks.

“I was being trained on a 747 to eventually use this plane to strike the White House,” Moussaoui said.

Part of the plan was to free Omar Abdel-Rahman, known as the “blind sheik” who was convicted in the 1993 bombing of the World Trade Center, and fly him to Afghanistan. If that failed, he said he planned to crash the plane into the White House.

Bin Laden told him to “remember your dream” and attack the White House, Moussaoui said in the statement.

Moussaoui was more subdued than in previous court appearances, when he lashed out at all court officials, but he became animated Friday when he complained that one of his lawyers “was going around saying, ‘Moussaoui is crazy, Moussaoui is crazy.”‘

Brinkema called him “an extremely intelligent man” who understood the nuances of conspiracy statutes.

But Moussaoui’s history of unpredictable behavior continued. He admitted that on Wednesday he said he would accept the death penalty, but had changed his mind and would now fight it.

Brinkema didn’t schedule a sentencing trial, saying many issues had to be settled first. Either side can insist on a jury trial, and Gonzales said the government hadn’t decided on a strategy.

In his statement, Moussaoui said he told al-Qaida associates that he would finish airline simulator training before September 2001 — an intriguing clue that he might have been part of the Sept. 11 plans.

The Sept. 11 Commission, which had access to the interrogations of top al-Qaida operatives in custody, found in its report that Moussaoui was “being primed as a possible pilot” in the attacks.

Moussaoui began flight lessons in February 2001 in an Oklahoma flight school. He also purchased two knives and flight deck videos for a 747 airliner and inquired about global positioning system equipment for aeronautical use, “activities that closely resembled the 9-11 hijackers,” the report found.

When Moussaoui entered the Minnesota flight school, his desire to fly large jets with so little training aroused suspicions. On Aug. 16, 2001, Moussaoui was arrested on immigration charges for overstaying his visa.

In one of the missed opportunities to foil the Sept. 11 attacks, one FBI agent concluded that Moussaoui was an Islamic extremist and potential airline hijacker. But top FBI officials didn’t see him as a major threat or link him to other warnings of an impending attack, and his arrest wasn’t publicized.

Bin Laden might have canceled the Sept. 11 attacks if he had known Moussaoui had been captured, one of the al-Qaida leaders later told interrogators.