The Pentagon announced last night it will quickly hold hearings for all 595 detainees at the Guantanamo Bay prison as it scrambles to respond to the Supreme Court ruling last week that the government was jailing terrorism suspects without due process.

The new hearings are designed to determine whether the 595 detainees at Guantanamo Bay, Cuba, meet the definition of "enemy combatants," as President Bush and the U.S. military have said for more than two years. The administration has used the enemy combatant designation to argue that the detainees do not warrant some protections afforded by the Geneva Conventions.

Since the prison for alleged terrorists opened in early 2002, some human rights activists have said that the government was obligated under international law to hold these hearings. But the government refused, saying the detainees did not deserve such rights because they are terrorists who wore no soldier's uniform and violated the laws of war by killing civilians.

The new hearings -- to be called Combatant Status Review Tribunals -- are separate from the hearings in federal court that the Supreme Court ruled the government must offer to all the inmates to contest their detentions. But administration officials and experts on military law said the new tribunals are designed to buttress the government's case -- that it has been deliberative in its detention decisions and afforded due process -- when it confronts defense attorneys in the federal court hearings.

"The administration is trying to make the best of a bad situation," said Eugene R. Fidell, president of the National Institute of Military Justice. "It's an effort to play catch-up ball, and to blunt the possible impact of the habeas corpus review."

The new tribunals were mandated by Deputy Secretary of Defense Paul D. Wolfowitz in an order signed yesterday. It establishes that by July 17, every detainee will be notified that his status as an enemy combatant will be reviewed in the new hearings, and that he has a right to a habeas corpus hearing in federal court. Each one will receive the help of a non-lawyer military officer acting as a "personal representative," who will assist him in preparing for the combatant status hearing.

Three neutral commissioned military officers -- none involved in the detainee's capture, detention or interrogation -- will hear each case, Wolfowitz ordered. The detainees will be allowed to attend all proceedings except for deliberations, and sessions in which national security could be compromised, the rules said. Detainees are to be given interpreters, and will be allowed to testify, present evidence, call witnesses "if readily available," and to question witnesses.

The three-officer tribunal will decide each detainee's case with "a preponderance of the evidence" required to uphold the military's stance that he is an enemy combatant. "There will be a rebuttable presumption in favor of the government's evidence," meaning that greater deference should be given to the military's claims but the detainee can try to argue against it.

If a prisoner is found not to be an enemy combatant, then he would be handed over to the State Department for transfer to his home country, officials said.

Wendy Patten, a representative of Human Rights Watch, said the rules are biased against detainees. "While the Geneva Conventions start with the presumption of greatest protection for the combatant . . . here it is the reverse -- they presume a detainee is an enemy combatant and expect him to disprove it."

The essential function of the new hearings, officials said, is to help government lawyers argue their cases for continued detention in the habeas corpus hearings that eventually will be held for all detainees. U.S. lawyers would be able to argue that there is no reason for a judge to inquire too deeply into a detainee's case because the government has already deliberated on it, legal experts said.

"When and if there are habeas petitions filed challenging their detention, the government will be in a position to say that we fully satisfied our legal obligations," a senior Justice Department official told reporters yesterday at a hastily convened news conference held on the condition that the speakers not be identified by name.

"The government here is reacting very quickly to the Supreme Court's decisions," the Justice Department official added.

The new combatant status tribunals also are not supposed to replace yet another type of hearing being planned for every detainee: an annual review of whether he remains a danger to the United States. These hearings, first planned after the Supreme Court announced it was going to hear the Guantanamo Bay case, are being overseen by Navy Secretary Gordon R. England and are expected to begin in coming months. Inmates found not to be a danger would be sent home.

In addition, six of the detainees at Guantanamo Bay are slated to be tried for crimes in front of a military court also called a tribunal. The Pentagon yesterday said nine additional prisoners are eligible for these trials.