In December 2003, German citizen Khaled el-Masri boarded a bus in Germany for a holiday in Skopje, Macedonia.

Instead of a restful vacation, the Muslim man of Lebanese heritage says he ended up in a Central Intelligence Agency isolation cell in Afghanistan as a suspected terrorist. He was released after five months of interrogation with no explanation justifying the action or apology if it was a mistake.

Now, nearly four years later, his lawyers are asking the US Supreme Court to examine whether the Bush administration has the power to prevent Mr. Masri from seeking recourse in American courts.

Masri's lawyers claim that the CIA kidnapped and tortured an innocent man. The government has never responded directly to the accusation. Instead, Justice Department lawyers asked a US judge to throw the case out of court to prevent disclosure of state secrets. He did.

At issue in El-Masri v. US is the government's use of the so-called state-secrets privilege. The judicial doctrine provides that some legal cases must be dismissed if the central evidence in the court battle would require disclosure of national security secrets. The Bush administration is using the same doctrine to block a string of legal challenges to other secret terror-war tactics, including warrantless electronic surveillance in the US.

Masri's lawyers say he is not seeking to disclose secrets; he just wants to have US officials held accountable for their alleged treatment of him, which has already been made public. The government counters that any effort to defend US actions in the Masri case would require disclosure of how the CIA handles terror suspects and other US intelligence sources and methods. Such information is secret and must remain secret, government lawyers say.

"It is true that, at a high level of generality, the government has disclosed the CIA's participation in a program involving detention and interrogation of suspected terrorists," Solicitor General Paul Clement says in his brief to the court. "But ... the facts that would be central to the adjudication of this action are not limited to such general disclosures."

Critics of the government's approach say the state-secrets privilege is being used to cover up Masri's alleged illegal detention and treatment. They add that it undermines the judiciary's oversight role in America's constitutional system of checks and balances.

"The whole reason for the court system is to protect individual rights that wouldn't be protected in the political process," says Amanda Frost, a visiting professor at Harvard Law School, who also teaches at American University's Washington School of Law.

If the high court takes up Masri's case, including the broader area of judicial responsibility, it could set the stage for a landmark ruling endorsing aggressive judicial oversight of secret administration tactics in the war on terror.

But that approach runs counter to the limited role for judges embraced by Chief Justice John Roberts and arguments by the solicitor general that judges have no business second-guessing presidential decisions concerning intelligence and war-fighting matters

When Masri filed his suit in federal court, government lawyers told the judge that just confirming or denying the charges would reveal state secrets about how the US is waging its war on terror. The government submitted a classified affidavit to the trial judge, explaining its position. Masri's lawyers were not permitted to see the affidavit.

The judge threw out the suit on state-secrets grounds, and a federal appeals court panel upheld the dismissal on the same grounds.

In his appeal to the Supreme Court, Masri is asking the justices to examine whether the government properly invoked the state-secrets privilege or simply used the privilege to avoid being held accountable for alleged torture and other illegal and unconstitutional activities.

"The [state-secrets] privilege is now routinely invoked to block adjudication of disputes that raise profound constitutional questions," says Benjamin Wizner of the American Civil Liberties Union, in his petition to the court.

He says the state-secrets privilege was originally meant to help resolve courtroom disputes over individual pieces of evidence. But the government is increasingly using the privilege as a way to immediately throw entire cases out of court, he says, before any investigation of the allegations can take place.

The Bush administration is urging the Supreme Court not to hear Masri's case. In a brief filed at the high court last week, Solicitor General Clement disputed suggestions that the administration has escalated its use of the state-secrets privilege. He also said the legal issues surrounding the privilege are clear and well settled.

"This court has already laid down the governing legal principles and ... the courts of appeals have consistently applied them to varying factual circumstances without demonstrating any need for further guidance," Mr. Clement writes in his brief.

The same state-secrets issue is also at the center of a string of lawsuits challenging the Bush administration's warrantless surveillance operations by the National Security Agency. The Ninth US Circuit Court of Appeals in San Francisco heard two cases last month involving alleged NSA surveillance within the US.

Although federal judges have reached conflicting rulings on how to apply the state-secrets privilege, so far appeals courts have uniformly upheld the Bush administration's position. Some analysts say that might soon change when the Ninth Circuit panel rules in the NSA cases.

Aside from the legal issue, the Masri case raises fundamental questions about fairness and respect for human rights by the US government, analysts say.

Masri's alleged ordeal sparked widespread outrage in Europe, triggered an ongoing German government investigation, and prompted an attempt by Secretary of State Condoleezza Rice to explain the Bush administration's position to allies. "When and if mistakes are made, we work very hard and as quickly as possible to rectify them," she told a 2005 press conference in Berlin.

But in the nearly two years since Ms. Rice's pledge, there has been no talk by the Bush administration of mistakes in the Masri case or rectification.

When he dismissed Masri's case on state-secrets grounds in 2006, US District Judge T.S. Ellis III said the action was required by settled, controlling law. But he added, "If El-Masri's allegations are true or essentially true, then all fair-minded people ... must ... agree that El-Masri has suffered injuries as a result of our country's mistake and deserves a remedy."

Some legal analysts also suggest new legislation could help resolve state-secrets disputes. The Classified Information Procedures Act was passed to help prosecute criminal cases in which some of the evidence is classified information. Under CIPA, a judge is empowered to substitute a nonclassified version of the same information as evidence for use in open court.

Some legal experts say Congress could write a new chapter to CIPA to permit similar protective procedures in civil cases filed against the US government involving classified information.