Civil liberties groups have strenuously protested at President Bush's decision to authorise the establishment of special military commissions. These would try captured members of al-Qaeda in the US or overseas. His order is likely to face constitutional challenge.
The commissions, which will have military juries with the right to impose the death penalty, will allow prosecutors to present evidence in secret to protect intelligence sources and will operate under less rigorous rules of evidence than the domestic courts.
The trials, which will not be subject to appeal, are likely to be quicker and defendants' rights of discovery are to be severely circumscribed.
Mr Bush, who signed the order on Tuesday before heading to Texas for the second part of his summit with Russia's President Putin, is said to regard the commissions as only an option in the US legal armoury. His emergency order does not require approval from Congress where strong concern has already been expressed about a ruling last week by the Attorney General allowing the police to listen in to lawyers' contacts with terrorist suspects.
The move reflected a real dilemma for the US which has rejected the establishment of a permanent international criminal court to try war criminals and whose domestic courts process would certainly prove unwieldy in such cases. Such trials could also now take place on well-protected military bases, easing security fears.
Unwieldy or not, civil libertarians question whether the message sent out that the US defends its cherished institutions by putting due process on hold may not be counter-productive.
European allies will certainly view the move with concern. They have supported the use of international tribunals, such as that at The Hague which on Tuesday jailed three more Bosnian prison guards for war crimes, arguing that such courts can legitimise the punishment of war criminals where national tribunals smack of victor's justice. They will also be concerned at the tribunals' right to impose the death penalty.
Military jurors might be more likely to vote for a death sentence, said Mr David B. Rivkin, a Washington lawyer who published a legal paper on Mr Bush's options this month. Convicted terrorists might be executed shortly after a trial, with few or none of the long delays for additional court appeals common in criminal courts, lawyers said.
The director of the Washington office of the American Civil Liberties Union, Ms Laura W. Murphy, said for a military trial to have constitutional legitimacy, Mr Bush must justify why ordinary courts could not do the job.
"Absent of such a compelling justification, today's order is deeply disturbing and further evidence that the administration is totally unwilling to abide by the checks and balances that are so central to our democracy," she said.
Military commissions date to the late 17th century, operating side by side with the better-known courts martial. The US last convened one on orders from President Franklin D. Roosevelt after German saboteurs secretly landed on US shores in 1942. Six of the nine were executed.
The Supreme Court upheld the proceedings, although lawyers say it is not clear whether that case would serve as a full precedent. An enemy who sneaked on to US soil "for the purposes of waging war by destruction of life or property" was a combatant who could be tried in a military court, the Supreme Court ruled then.
Detention and trial of accused terrorists by a military tribunal is necessary "to protect the United States and its citizens, and for the effective conduct of military operations and prevention of terrorist attacks", Mr Bush's five-page order said.
A senior Justice Department official told Associated Press that only non-citizens would be tried before the commission.
