WASHINGTON — The Bush administration has instructed American diplomats abroad to defend its decision to seek the death penalty for six Guantanamo Bay detainees accused in the September 11, 2001 terror attacks by recalling the executions of Nazi war criminals after World War II.

A four-page cable sent to American embassies says that execution as punishment for extreme violations of the laws of war is internationally accepted and points to the 1945-46 International Military Tribunals as an example. Twelve of Adolf Hitler’s senior aides were sentenced to death at the trials in Nuremberg, Germany, although not all were executed in the end.

The unclassified cable was sent by the State Department to all American diplomatic missions worldwide late yesterday.

In it, the department advises American diplomats to refer to Nuremberg if asked by foreign governments or media about the legality of capital punishment in the September 11 cases.

“International Humanitarian Law contemplates the use of the death penalty for serious violations of the laws of war,” the cable, which was written by the office of the department’s legal adviser, John Bellinger, says.

“The most serious war criminals sentenced at Nuremberg were executed for their actions,” it said.

The cable makes no link between the scale of the crimes perpetrated by the Nazis, which included the Holocaust that killed some 6 million European Jews and other minorities, and those allegedly committed by the Guantanamo detainees, who are accused of murder and war crimes in connection with September 11, in which nearly 3,000 people died.

But it makes clear that the American administration sees Nuremberg as a historic precedent in asking for the September 11 defendants to be executed.

The decision to seek the death penalty for these defendants is likely to draw criticism from the international community. A number of countries, including American allies, have said they would object to the use of capital punishment for their nationals held at Guantanamo.

The cable is written in a question-and-answer format in anticipation of inquiries that diplomats may get from foreigners about the Pentagon’s announcement of the trial and charges.

“Posts are asked to draw from the points provided below in responding to foreign government and media requests regarding this announcement,” it says in a one-paragraph summary under the subject heading: “Q and A – Guantanamo Detainees Charged for 9/11.”

Much of the cable is taken up with descriptions of the defendants and the allegations against them as well as assurances they will receive fair trials.

The Nuremberg reference is in the response offered to the sample question: “Doesn’t the application of the death penalty to these defendants violate international law?”

The one-word answer provided before the explanation that invokes Nuremberg: “No.”

The unprecedented proceeding will be the first capital trial under the terrorism-era American military tribunal system.

Despite the confidence of military prosecutors, the case has been clouded by revelations that the key suspect, Khalid Sheikh Mohammed, the suspected mastermind of the attacks in which hijackers flew planes into buildings in New York and Washington, was subjected to harsh interrogation tactics.

The cable refers specifically to this and instructs diplomats to advise foreign governments that the tribunal will not accept evidence obtained through torture and that the defendants can raise objections to any statements they argue they made under coercion. Those decisions will be up to the judge, it says.

But it notes a distinction between torture and “cruel, inhuman and degrading treatment” that was outlawed by legislation sponsored by Senator McCain, now the leading Republican candidate for the 2008 presidential nomination and a former prisoner of war during Vietnam.

The cable informs diplomats that statements made by defendants under such conditions before the passage of the Detainee Treatment Act of 2005 may be considered by the court.

Of the accused, at least one, Khalid Sheikh Mohammed, was arrested and interrogated before that law was passed. At least one other, Mohammed al-Qahtani, who officials have labeled the 20th hijacker, claims to have been mistreated under questioning.

“For evidence obtained before the enactment of the McCain Amendment, where there is an allegation that evidence has been obtained through coercive means, it is inadmissible unless the judge” makes a specific determination that it is “reliable,” “probative,” and that “the interests of justice would best be served by the statement’s admission,” it says.

The cable adds that a decision to allow such evidence could be appealed to American federal courts should a defendant be convicted.