SAN JUAN, Puerto Rico – The American military suspended a pretrial hearing for a Guantanamo Bay detainee accused of killing an American Green Beret, saying yesterday that base security first had to help investigate the recent deaths of three detainees.

Two Saudis and a Yemeni hanged themselves in their cells on June 10, according to the military. Their bodies were flown aboard a commercial charter jet Friday from the American base in Cuba to Yemen and Saudi Arabia. They were the first reported detainee deaths at the prison since it opened in January 2002.

The pretrial hearing for a Canadian detainee, Omar Khadr, was scheduled to begin June 26. The Toronto native is charged with murder and other crimes for allegedly throwing a grenade that killed an American Special Forces soldier in Afghanistan and for planting mines targeting American convoys.

A cloud of uncertainty also hangs over the Guantanamo Bay hearings as the Supreme Court decides whether the Bush administration overstepped its authority in ordering military trials for suspected Al Qaeda and Taliban terrorists. The court will rule before June 30.

The first military trials held by America since World War II are slated to begin in the fall. Mr. Khadr is one of 10 detainees charged with crimes. About 460 men are held at the isolated base in eastern Cuba.

“We’re all waiting on what the decision is, and what the scope of the decision is,” one of Mr. Khadr’s defense attorneys, Marine Lieutenant Colonel Colby Vokey, said.

The Office of Military Commissions said the postponement of pretrial hearings was being extended through July 7.

An office spokeswoman, Major Jane Boomer, said guards at Guantanamo bring detainees to and from the small courthouse and provide security during pretrial hearings.

Major Boomer said the office decided it was better to have the guards first assist in the investigations of the deaths of the detainees, whose family members have claimed the men were killed by Americans.

“The court sessions are a tremendous strain on security,” Major Boomer said in a telephone interview from the Pentagon. “The investigation of the recent suicides … takes priority.”