GUANTANAMO BAY NAVY BASE, Cuba -- Opening the United States' first war crimes trial since World War II, the government on Tuesday charged a wiry Yemeni who worked as Osama bin Laden's chauffeur with conspiracy as a member of the al Qaeda terrorism network.

The first Military Commission in the 3-year-old war on terrorism also marked the first time a captive held in the Guantánamo prison was publicly displayed and formally charged.

Salim Hamdan, 34, did not enter a plea, pending defense arguments expected in November. But he has admitted through his lawyer to driving bin Laden around his farm in Kandahar, Afghanistan.

He denies joining his boss' worldwide movement, trying to kill an American or carrying a gun - before or after the Sept. 11 attacks that prompted President Bush to declare a war on terrorism and set up the offshore interrogation prison camp, and, ultimately, this week's tribunals.

LED INTO COURT

At first seeming dazed, Hamdan, who has been held for more than two years, flashed a toothy grin when he was led unshackled into the courtroom, guarded by two soldiers in battle dress.

With a trim, wispy mustache and receding hairline, he wore traditional clothes his family had sent from home: a floor-length white gown topped by a black-and-brown-checked jacket and a white woven head scarf, called a keffiyah, draped over his shoulders.

He stood beside his Pentagon defense lawyer, dressed in Navy whites, while he heard the charges against him read in Arabic. When he was asked whether he understood the charges of conspiracy to murder, attack civilians and commit terrorism, he grinned again.

Hamdan knows the charges carry sentences of life in prison, said his lawyer, Lt. Cmdr. Charles Swift, who described Hamdan's grins as expressing a mix of confusion over the concept of conspiracy and joy at being with others after months of solitary confinement.

Pentagon charge sheets alleged that Hamdan, who has a fourth-grade education, a wife and two daughters, transported weapons to al Qaeda operatives, trained at an al Qaeda camp and drove in convoys that carried bin Laden. They do not accuse him of any specific violence or planning any attacks.

Swift, who is paid by the Pentagon, says his client is eager to prove his innocence. Meanwhile, he is challenging the military trials in civilian U.S. courts.

The daylong session lasted more than eight hours and mostly was consumed with sparring between Swift and the presiding officer, Army Col. Peter Brownback III, over the suitability of the six military officers judging the case.

It reflected the controversy that surrounds these trials, a Bush administration fusion of pre-World War II military justice and post-Sept. 11 security rules that permit both secret and hearsay evidence.

"We've spent a lot of money to get six people here to look at Mr. Hamdan across this table, " Brownback said of the five commission members and single alternate who will decide both the law and facts in the case. "We're here so six people can carry out the president's order - to provide a fair trial for Mr. Hamdan."

MEMBERS CHALLENGED

Swift formally challenged five panel members, including Brownback, saying their military pasts might preclude objectivity. Brownback rejected his challenges but noted that a final decision will be made in Washington by retired Maj. Gen. John Altenburg Jr., a lawyer appointed to oversee the trials by Defense Secretary Donald Rumsfeld.