MIAMI (Reuters) - Two alleged al Qaeda bomb makers make their first appearances before a U.S. military tribunal at the Guantanamo navy base this week, as the U.S. Supreme Court prepares to decide whether the tribunals are legitimate.

A Yemeni said to have been a bodyguard for Osama bin Laden is also scheduled to appear in hearings that begin on Wednesday at the remote and controversial U.S. base in southeast Cuba.

The trio are among only 10 prisoners charged with crimes at the camp, which holds nearly 500 foreign captives and which UN human rights investigators have urged Washington to shut.

Guantanamo has long been a focal point of criticism of the United States, with accusations that the mostly Muslim detainees have been tortured and humiliated -- charges military officers at the base deny.

U.S. federal judges halted three of the trials pending a U.S. Supreme Court ruling on whether President George W. Bush had authority to create the tribunals to try foreign terrorism suspects after the September 11 attacks.

The Supreme Court is scheduled to hear arguments in the case on March 28 and to rule in June or July. Defense lawyers have argued against holding more hearings at Guantanamo now when the whole tribunal process could be declared moot.

"It would seem there would be some advantages to waiting to see what the Supreme Court does," said Col. Dwight Sullivan, the chief defense counsel for the tribunals, which are formally called military commissions.

But the Pentagon is proceeding with the other seven cases, apparently because no one ordered it not to.

"There is no judicial stay in the other seven cases," said Maj. Michael Shavers, a Pentagon spokesman.

On the docket this week are Sufyian Barhoumi, an Algerian, and Ghassan Abdullah al Sharbi, a Saudi, who are to be arraigned on charges of conspiring with bin Laden and al Qaeda to attack civilians, commit murder and destroy property.

EXPLOSIVES TRAINING

Both are accused of attending al Qaeda camps where they trained to make electronically controlled explosives. The charges say al Sharbi met bin Laden at one camp and stood guard with loaded weapons while the al Qaeda leader visited.

In March 2002, the pair went with al Qaeda operations director Abu Zubaydah to a guest house in Faisalabad, Pakistan, where Barhoumi trained al Sharbi and another Guantanamo defendant to build remote, hand-held detonators for bombs to be used against U.S. forces in Afghanistan, the charges said.

Zubaydah gave the group $1,000 to shop for electronic parts and assemble circuit boards for use as bomb timers, according to the charges.

Al Sharbi and Bahroumi were captured with Zubaydah during a raid on March 28, 2002. Zubaydah is in U.S. custody at an undisclosed location and believed to be cooperating with investigators.

Yemeni Ali Hamza al Bahlul, who acknowledged during a hearing that he is "from al Qaeda," is also scheduled to appear before a tribunal this week.

He is accused of conspiring to commit war crimes by acting as a bin Laden bodyguard and making al Qaeda recruiting videos. During a hearing in January, Bahlul said he did not recognize the authority of what he called an illegal tribunal set up by enemies of the Muslim nations.

He held up a sign declaring "boycott" and said he would remain silent, after reading a lengthy list of complaints.

The tribunals are the first held by the United States since World War Two and convened in August 2004, over 2-1/2 years after the first prisoners were brought to Guantanamo. None has reached the trial stage, partly because of court challenges.

Defense attorneys and human rights groups argue that any charges should be brought in civilian courts or the military courts-martial system, rather than the tribunal system, where the rules are in flux.