US officials did not violate any clearly established constitutional rights when they held a US citizen in isolated military detention without charge for nearly four years and subjected him to harsh interrogation techniques.

That's the legal position staked out by Justice Department lawyers who are urging a federal judge in Charleston, S.C., to dismiss a lawsuit filed on behalf of Jose Padilla against former Defense Secretary Donald Rumsfeld and nine other current or former US officials. Mr. Padilla was held in military custody from 2002 to 2006 as a suspected Al Qaeda operative and enemy combatant.

The 55-page motion, filed this week, offers the first detailed defense of the government's aggressive treatment of Padilla during his three years and seven months in military custody. Padilla's suit says he endured isolation, stress positions, extreme cold, sleep deprivation, and reportedly was subjected to five months of severe sensory deprivation, including near total isolation from human contact.

Mental-health experts who have examined Padilla say the experience has left him with severe mental disabilities, including post-traumatic stress disorder.

Government lawyers made no reference to Padilla's diagnosed psychological problems. They told US District Judge Henry Floyd that such a lawsuit, if allowed to progress, would interfere with military decisionmaking, aid the enemy, and make the US more vulnerable to terrorist attack.

"It would be difficult to devise a more effective fettering of executive branch officials than to allow enemy combatants to trade a battlefield in Afghanistan for a battlefield in the US legal system," Barbara Bowens, civil chief of the US Attorney's Office in South Carolina, says in her brief.

After nearly four years in military custody, Padilla was transferred to the criminal-justice system in January 2006. He was convicted in August in a Miami terror-conspiracy trial and is set to be sentenced in December. An appeal is expected.

Although Padilla was placed on trial and convicted in Miami, no court has fully assessed the legality of Padilla's earlier detention and interrogation in military custody. Government lawyers say such an assessment is unwarranted.

"Padilla's designation, detention, and interrogation as an enemy combatant did not violate any clearly established constitutional rights," Ms. Bowens says in her brief.

"It cannot be said that there were any constitutional 'bright lines' applicable to Padilla's case which the [government] could be held liable for transgressing," Bowens writes.

The issue of "clearly established" rights is important because government officials are protected by immunity from such lawsuits even when rights may have been violated. They lose that immunity, however, if the violated rights are so obvious to a reasonable person that they are considered "clearly established."

"Officials are not liable for bad guesses in gray areas," Bowens notes. "They are liable for transgressing bright lines."

Padilla's lawyers believe the lines in his case are clear and clearly established. In their 30-page complaint, they charge that Padilla "suffered gross physical and psychological abuse at the hands of federal officials as part of a scheme of abusive interrogation intended to break down [his] humanity and his will to live."

The complaint says US officials violated Padilla's constitutionally protected rights to consult a lawyer, to gain access to the courts, to practice his religion and associate with family and friends without government interference, and to be free from coercive interrogation, free from cruel and unusual punishment, and free from illegal and arbitrary detention.

Fundamentally at issue in the Padilla case is whether such constitutional guarantees continue to protect a US citizen seized on US soil and held without charge in a US-based military prison once the citizen is designated an enemy combatant.

Bowens says the issue has already been decided by a federal appeals-court panel in Richmond that upheld Padilla's military detention in September 2005. As a result, she says, Padilla's lawyers should be precluded from raising any constitutional claims – even claims related to Padilla's interrogation and isolation.

Some legal analysts say they are alarmed by the sweep of the government's position. "The notion that there is absolutely no limit in how the government treats US citizen detainees strikes me as a disturbing proposition," says Stephen Vladeck, a law professor at American University in Washington, D.C. "Most people would have thought before the Padilla case that the government can't simply do whatever it wants to a US citizen in military custody."

Given the government's reliance on "clearly established" law, the Padilla civil case could present an ironic twist in the long and heated debate over Bush administration tactics in the war on terror. White House and Justice Department officials worked hard in the years since the 9/11 attacks to maximize legal flexibility in dealing with detainees. They sought to clarify the law in a way that would protect interrogators, soldiers, and other US officials from civil suits and war-crimes charges.

Instead of clarification, the efforts triggered debates both within and outside the administration over what the law should be.

Now, legal analysts say, the administration may rely on the lingering uncertainty to help shield US officials from legal liability. "It will make it a lot harder for plaintiffs [like Padilla] to win a lawsuit because there is a much better argument that the relevant laws aren't clearly established," Professor Vladeck says.

"Even though Padilla's rights may have been violated, the real question is whether it was clearly established that what the government was doing to him was illegal," Vladeck says. "One can't help but wonder based on the torture debate whether anything was clearly established."