MIAMI — Critics of the war-crimes tribunal at Guantanamo Bay have consistently assailed the coerced confessions that may be used as evidence against the defendants and repeatedly charged that the prisoners’ severe isolation causes mental illnesses that make them unable to aid in their own defense.

Now, the critics add, evidence has emerged to show that the government advised interrogators to destroy their notes to evade legal consequences for their actions.

As the Bush administration revs up its prosecution of terror suspects ahead of the November election, defense lawyers and human rights advocates are ratcheting up their criticism of the offshore justice system.

The Senate Judiciary Committee heard testimony yesterday about abuse of prisoners at Guantanamo and demands that all American interrogators renounce coercive techniques.

“Cruel, inhuman, and degrading treatment of prisoners under American control violates our nation’s laws and values,” Senator Feinstein, the California Democrat chairing the committee, said.

“It damages America’s reputation in the world and serves as a recruitment tool for our enemies,” Ms. Feinstein said. “Perhaps most importantly, it has also limited our ability to obtain reliable and usable intelligence to help combat the war on terror, prevent additional threats, and bring to justice those who have sought to harm our country.”

Ms. Feinstein and the federal lawyers and agents who addressed the committee called for the shutdown of Guantanamo and transfer of the terrorism suspects’ trials to U.S. federal courts.

The renewed condemnation of coercive interrogation techniques followed the disclosure earlier this week that the Pentagon had advised federal agents to destroy any written records of their attempts to exact confessions or intelligence from terrorism suspects.

Lieutenant Commander William Kuebler, the Navy lawyer defending young Canadian prisoner Omar Khadr, encountered the directive in an unclassified portion of the 2003 Guantanamo “standard operating procedures” manual that was in effect at the time Mr. Khadr was interrogated at the American naval base in Southern Cuba.

Because the mission “has legal and political issues that may lead to interrogators being called to testify, keeping the number of documents with interrogation information to a minimum can minimize certain legal issues,” the manual noted.

Commander Kuebler said the absence of written records of Mr. Khadr’s interrogations at Guantanamo and at Bagram air base in Afghanistan, where he was taken after being wounded and captured in July 2002, deprives him of a basis for contesting alleged confessions. He said he would file a motion to dismiss murder and terror conspiracy charges against his client.

The judge hearing Mr. Khadr’s case for the past year, Army Colonel Peter Brownback, was dismissed two weeks ago. Though the tribunal’s chief judge said his departure was due to Colonel Brownback’s plan to leave active duty in June, some observers connect his replacement with his refusal to set a trial date until the prosecution produced documents sought by the defense, including the interrogation notes.