The United States military formally opened its first trial of an accused al Qaeda collaborator Tuesday, alleging that the former personal chauffeur for Osama bin Laden helped him ferry weapons and flee after the 1998 bombings of U.S. embassies in East Africa and the Sept. 11, 2001, terrorist attacks.

As the first military tribunals since the end of World War II got underway, the Pentagon-appointed defense lawyer for Salim Ahmed Hamdan attacked the process as unfair and assailed the presiding officer, calling him unqualified to serve. In a rare move, the attorney, Lt. Cmdr. Charles Swift, asked Army Col. Peter E. Brownback III to step down from the case.

Swift also questioned whether several other members of what the Pentagon calls "military commissions" could serve as independent jurors, and requested that they be disqualified as well. They include an officer who served in intelligence operations in the Middle East, another who sent detainees from Afghanistan to Guantanamo Bay, a third who commanded a Marine who perished in the World Trade Center attack and a fourth who said he could not say with certainty what the Geneva Conventions are.

Hamdan, 34, was escorted into a makeshift courtroom at the U.S. Navy base here wearing a flowing white shawl, a traditional Yemeni jilbab scarf wrapped around his head and a white, black and tan checkered sports coat that was two sizes too big. Hamdan removed the jilbab from his head, rested it upon his shoulders and broke into a broad smile when he spotted Swift standing at the defense table.

Hamdan has been in Guantanamo for nearly three years, the last eight months in an isolation camp. He seemed slightly overwhelmed as he scanned the rows of seats filled with military officers, reporters, human rights advocates and others. He turned to the spectators, giving them a quick nod and a smile before turning back to face the members of the military commission who have been assigned to hear the charges against him. If convicted of conspiring to commit war crimes, Hamdan faces life in prison.

"Are you prepared to go forward?" Brownback asked.

"I agree," Hamdan said through an interpreter.

Hamdan's appearance marked the first time that military commissions have been used by the United States since World War II. Two months after the Sept. 11, 2001, terrorist attacks, President Bush ordered that suspected terrorists and Taliban fighters captured in Afghanistan and elsewhere be tried before the commissions.

Initial hearings for the first four suspects facing trial are being held this week at the Guantanamo Bay base, where 585 suspected al Qaeda and Taliban fighters are detained. Eleven other detainees have been designated for trials before the commissions. They are awaiting formal charges and hearing dates.

A hearing is scheduled Wednesday for David Hicks, 29, an Australian kangaroo skinner who converted to Islam and allegedly joined al Qaeda after watching the attacks of Sept. 11. His father, Terry Hicks, 58, landed at Guantanamo Bay Tuesday after a 30-hour flight to see his son for the first time in years.

David Hicks has been detained here for nearly three years, and his father said he was not sure what to say when he sees him in the courtroom. "At this point, it hasn't hit home yet," Terry Hicks said.

Administration officials say the trials will be fair, but military lawyers and human rights and civil liberties groups call them relics. They say that the rules and procedures stand in sharp contrast to military courts-martial and internationally accepted laws of war, and that they carry the potential of diminishing the perception of the U.S. justice system around the world.

In commission hearings, defense lawyers and prosecutors are permitted to question the qualifications of panelists under a voir dire process similar to the ones used in military courts-martial and civilian courts. Because the commission members serve as jurors, prosecutors and defense lawyers can probe whether the panelists have potential conflicts or biases that could influence their decision making during the trial and deliberations.

After his occasionally testy questioning of Brownback, Swift asked the presiding officer to disqualify himself. Swift said Brownback let his law license lapse, would exert improper influence over other commission members because he was a military lawyer and judge for 27 years, had multiple contacts with the military officer supervising the commissions, and had formed an opinion on whether suspected terrorists and Taliban fighters should have the right to speedy trials.

"We challenge the presiding officer," Swift said, adding that he discovered a tape of a conversation in which Brownback reportedly stated his opinion about detainees' rights to a speedy trial.

The disclosure of the tape appeared to take Brownback by surprise. Still, he said he would forward Swift's challenge and the tape to John D. Altenburg Jr., a retired Army major general who serves as the supervisor of the commissions and will decide whether to dismiss Brownback.

Brownback declined to halt the proceedings while a decision is pending. "I will not hold the proceedings in abeyance," he said.

Swift and the military prosecutor, Navy Cmdr. Scott M. Lang, later began to question the remaining members of the commission: four panelists and one alternate, all military officers. Swift ultimately asked five of the six commissioners, including Brownback, to step down.

Swift questioned Air Force Lt. Col. Timothy Toomey, an intelligence officer who was involved in operations in Afghanistan and Iraq, and Marine Col. R. Thomas Bright, who supervised an operation that sent suspected terrorists and Taliban fighters to Guantanamo Bay. Each said he could be fair-minded during the proceedings.

Swift also questioned Marine Col. Jack K. Sparks Jr., who said he had lost one of his reservists in the attack on the World Trade Center. The Marine reservist was a firefighter, and the commission member attended his funeral and visited Ground Zero a few weeks after the attack.

"Were you angry?" Swift asked.

"I would imagine that everyone who saw it was angry," Sparks responded.

Swift concluded the questioning by turning to Army Lt. Col. Curt S. Cooper. At one point, he asked Cooper if he knew what the Geneva Conventions were.

"Not specifically, no, sir," Cooper responded, prompting Swift to call him unqualified to serve and to ask for his removal as well.

Salim Ahmed Hamdan, 34, was formally charged at Guantanamo Bay with conspiracy as an al Qaeda member to commit war crimes.