The arguments could lead to the most significant ruling on presidential war powers since the World War Two era.

At issue are special war crimes tribunals Bush established shortly after the September 11 attacks for trying prisoners held at the U.S. military base at Guantanamo Bay in Cuba.

The case could further define the balance of power between the presidency and the judiciary after Supreme Court rulings in 2004 that put limits on Bush's powers in the war on terrorism.

Lawyers for Salim Ahmed Hamdan, a Yemeni who was bin Laden's driver in Afghanistan, have argued that Bush lacked the power to create the tribunals.

The court will also consider whether Guantanamo prisoners can go to court in the United States to enforce protections under the Geneva Conventions. The Bush administration says the conventions do not apply to these prisoners.

Georgetown University law professor Neal Katyal, who is arguing the case for Hamdan, challenged the tribunals as unlawful because they failed to provide the same fair procedures and protections as U.S. and international law.

The administration says the president has the power to set up the tribunals based on his authority as commander in chief and on a resolution approved by the U.S. Congress authorizing military force after the September 11 attacks.

Solicitor General Paul Clement of the Justice Department, who will try to defend Bush's broad powers in the war on terrorism, said the Geneva Convention's protections do not apply to al Qaeda members like Hamdan.

Before the justices can rule on the legal issues at the heart of the case, they must decide a more basic question -- whether a recent law stripped the court of its jurisdiction over Hamdan's appeal.

The administration said Hamdan's challenge must be dismissed because of the Detainee Treatment Act that Bush signed on December 30. Hamdan's lawyers said the law was not meant to sidetrack an existing challenge to the tribunals.

The Hamdan case will be heard without Chief Justice John Roberts. He has removed himself because before he joined the Supreme Court he was part of a U.S. appeals court panel that ruled against Hamdan.

© Reuters 2006