WASHINGTON - Observers at the Supreme Court on Wednesday should probably be excused in advance for concluding that they have wandered into a time warp.

The question before the court will be whether federal judges have jurisdiction to hear cases brought by detainees at Guantánamo Bay, Cuba. A lawyer for a group of detainees will argue that they do; the Bush administration's solicitor general will argue that they do not.

But did not the court already decide that question? Did not the justices rule in Rasul v. Bush in 2004 that federal judges could review the legality of the Guantánamo detentions, rejecting the administration's position that the detainees' fate was a question for the executive branch alone?

No, history will not just be repeating itself at the court Wednesday. It has moved on, and the four years since the court shocked the administration by agreeing to hear the Rasul case have been busy ones.

Each of the three branches of government has made a series of judgments on how to strike the balance between individual liberty and national security in the post-9/11 era. This latest Supreme Court confrontation, round three of the justices' encounter with the detainee question, reflects an extraordinary interbranch drama, played out as a series of actions and reactions that has now cycled back to where it began: the role of the federal courts.

This third round is potentially the most momentous, because at stake is whether the Supreme Court itself will continue to have a role in defining the balance or whether, as the administration first argued four years ago, the executive branch is to have the final word.

The roots of the new case, Boumediene v. Bush, No. 06-1195, lie in the court's second-round detainee case, Hamdan v. Rumsfeld, decided in 2006. The court ruled that the military commission system the Bush administration had set up to try enemy combatants for war crimes was fatally flawed because the president had acted without Congressional authorization.

That decision came in an appeal brought by Salim Ahmed Hamdan, a former driver for Osama bin Laden. Mr. Hamdan's route to court had been by means of a petition for habeas corpus, the traditional route for prisoners to get before a judge to challenge the validity of their confinement.

In its waning weeks under Republican control, Congress responded swiftly to the Hamdan decision by passing the Military Commissions Act of 2006. This new law not only authorized the military commissions - a commission at Guantánamo will begin taking evidence against Mr. Hamdan on Wednesday - but also provided that "no court, justice or judge shall have jurisdiction to hear or consider" further habeas corpus petitions from foreigners held as enemy combatants, at Guantánamo or anywhere else.

Now the question before the Supreme Court is whether that court-stripping action was valid in light of the Constitution's injunction to Congress not to suspend "the privilege" of habeas corpus "unless when in cases of rebellion or invasion the public safety may require it."

No one disputes that those conditions have not been met. But resolving the challenge to the Military Commissions Act is not as simple as stating that obvious fact.

Modern Supreme Court decisions have put a gloss on the "suspension clause," as the constitutional provision is known, holding that habeas corpus need not be available in a formal sense as long as prisoners have an "adequate and effective" substitute for challenging the validity of their detention. The government offers a substitute: "combatant status review tribunals," which are panels of military officers who review the initial determination that an individual detainee has been properly labeled an enemy combatant.

As substitutes for habeas corpus, the tribunals are "structurally and incurably inadequate," Seth P. Waxman, a lawyer for six Algerian detainees, asserts in his brief. By sharply limiting access to evidence and witnesses and by forbidding defense lawyers from participating in the hearings, he says, the alternative procedure fails to offer "even the most elemental aspects of an independent adversarial proceeding."

Mr. Waxman, who served as solicitor general in the Clinton administration, will argue on behalf of the four groups of detainees whose separate cases have been consolidated for a single argument. The current solicitor general, Paul D. Clement, will argue for the government. It will be Mr. Clement's fourth argument in a detainee case; he argued the Hamdan case last year and, as principal deputy solicitor general, also argued a pair of cases that the court heard along with the Rasul case in 2004.

The government's position is that the detainees' complaints about the alternative procedure are irrelevant. Mr. Clement argues that the Military Commissions Act has rendered moot the court's 2004 decision that federal judges had jurisdiction over cases from Guantánamo. That ruling, in the Rasul case, simply interpreted the federal habeas corpus statute as it then existed, he says, before the Military Commissions Act amended the statute to withdraw jurisdiction.

Without a statutory basis for jurisdiction, the government's argument continues, there is no jurisdiction because as "aliens with no connection to this country who were captured abroad in the course of an ongoing military conflict," the detainees can claim no constitutional entitlement to habeas corpus.

In any event, the alternative procedure is more than adequate, Mr. Clement asserts in the government's brief, enabling the detainees to "enjoy more procedural protections than any other captured enemy combatants in the history of warfare."

The government's argument persuaded the United States Court of Appeals for the District of Columbia Circuit, which ruled in February that the Military Commissions Act had succeeded in removing the federal courts' habeas corpus jurisdiction. In April, the Supreme Court initially turned down the detainees' appeal of that ruling, before reversing itself in a startling about-face on the final day of its term in June.

The Algerians whom Mr. Waxman represents are among 34 detainees in the current case. The others include a Libyan, a Palestinian, 4 Kuwaitis and 22 Yemenis, who represent the biggest national group among the 300 or so men being held at Guantánamo. Most of those before the court were captured in Afghanistan or Pakistan by bounty hunters or local tribes who turned them over to United States forces.

The Algerians are an exception. Lakhdar Boumediene and the other five immigrated to Bosnia during the 1990s and were legal residents there. They were arrested by Bosnian police in October 2001 on suspicion of plotting to attack the United States embassy in Sarajevo.

The Supreme Court of Bosnia and Herzegovina ordered them released three months later for lack of evidence. The Bosnian police seized them immediately and turned them over to the United States military, which transported them to Guantánamo.

Mr. Waxman is arguing that because these six do not fit any authorized definition of enemy combatant, the Supreme Court should order their release.

If the court rules for the detainees, a more likely result is an order to the appeals court to consider for the first time the merits of the men's habeas corpus petitions. The government would then almost certainly renew the argument it made in the immediate aftermath of the Rasul decision: that even assuming the existence of the federal courts' jurisdiction, the detainees had no constitutional rights that they could assert. That question, which the justices have not directly confronted in any of the cases so far, would then almost certainly come back to the Supreme Court.

The vote in the Hamdan case last year was 5 to 3. Chief Justice John G. Roberts Jr. did not participate, because he had voted in the case, on the government's side, when he was a judge on the appeals court. The dissenting justices were Antonin Scalia, Clarence Thomas and Samuel A. Alito Jr., voting in his first detainee case.

The conventional wisdom that the outcome of the new case will depend on the vote of Justice Anthony M. Kennedy is almost certainly correct.

Justice Kennedy has been in the majority in the other detainee cases and, quite likely, gave a signal in June that gave the more liberal justices the confidence to add the case to the court's docket with some assurance of the likely outcome.

Some of the many briefs filed for the detainees address arguments to Justice Kennedy.

Limiting access to lawyers presents a danger to individual rights and a "severe impairment of the judicial function," the New York City Bar Association says in a brief addressed to the prohibition on lawyers participating in the review tribunals. The quotation is from a 1991 Supreme Court decision that struck limitations placed on Legal Services Corporation lawyers. Justice Kennedy was the decision's author.

© 2007 The New York Times