GUANTANAMO BAY NAVAL BASE, Cuba - Khalid Shaikh Mohammed said yesterday that he would confess to masterminding the Sept. 11 attacks, throwing his death-penalty trial into disarray and shocking victims' relatives who watched from behind a glass partition.

Four other alleged Sept. 11 conspirators also abandoned their defenses, in effect daring the Pentagon to grant their wish for martyrdom. The judge ordered lawyers to advise him by Jan. 4 whether the Pentagon can apply the death penalty - which military prosecutors are seeking - without a jury trial.

"When they admitted their guilt, my reaction was, 'Yes!' My inclination was to jump up and say, 'Yay!' But I managed to maintain my decorum," said Maureen Santora of Long Island City, N.Y., whose firefighter son Christopher died responding to the World Trade Center attacks.

Santora was one of nine victims' relatives watching the Guantanamo proceedings, the first time that relatives of the 2,975 people killed in the attacks have been allowed to observe the war-crimes trials.

In an about-face that appeared to take the court by complete surprise, the five men announced they were abandoning their attempts to mount a vigorous defense and instead requested "an immediate hearing session to announce our confessions."

The confessions were delayed, however, when the judge said that two of the defendants, Ramzi Binalshibh and Mustafa al-Hawsawi, could not enter pleas until the court determines their mental competency. The three others said they would wait as well.

"Our plea request was based on joint strategy," said defendant Ali Abd al-Aziz Ali, also known as Ammar al Baluchi. The fifth defendant is Walid bin Attash.

In a letter read aloud by the judge, the defendants implied that they wanted to plead guilty but did not specify whether they would admit to specific charges.

Their letter was so unexpected that the judge, Army Col. Stephen Henley, was unsure how to proceed. He noted that the law specified that only defendants unanimously convicted by a jury could be sentenced to death in the tribunals. No jury has been seated.

"It seemed like a real bombshell to me," said Alice Hoagland of Redwood Estates, Calif., whose son Mark Bingham is believed to be among the passengers who fought hijackers on United Flight 93 before it crashed in Western Pennsylvania.

She told reporters she hoped that President-elect Barack Obama, "an even-minded and just man," would ensure that the five men are punished, though she stressed that wouldn't heal the loss of her son.

Mohammed, who has already told a military panel he masterminded the attacks, said he had no faith in the judge, his Pentagon-appointed lawyers or President Bush. Sporting a chest-length gray beard, Mohammed told the judge in English: "I don't trust you."

The five defendants said they decided on Nov. 4 - the day Obama was elected - to abandon their defenses against the capital charges. Obama opposes the trials and has pledged to close the detention center.

Even if trials are held, it is unlikely any would be completed before Obama takes office Jan. 20. Still, the U.S. military is pressing forward with the case until it receives orders to the contrary.

Human-rights observers said the judge's uncertainty about sentencing highlighted problems with America's first war-crimes trials since World War II, and was further evidence that they should be shut down, as Obama has pledged to do.

"The fact that the judge doesn't know whether they can be sentenced to death in one of the most important trials in U.S. history shows the circuslike atmosphere of the military commissions," said Jennifer Daskal of Human Rights Watch. "These cases belong in federal court."