(CBS) The Pentagon's system of military tribunals is ready to begin work, but a key component is missing: defendants.

Lawyers familiar with the matter say they believe only a small number of the approximately 660 detainees captured in the war on terrorism and held at Guantanamo Bay, Cuba, will ever appear before the U.S. military tribunals.

The rest will go home either as free men or to face charges in the countries where they are citizens.

Countries that have said publicly they want their citizens home from Guantanamo include Russia, Saudi Arabia, Sweden, Britain and Pakistan.

Guantanamo Bay is a likely location for any U.S. military commission trials. The Pentagon has listed 18 war crimes and eight other offenses that could be tried, including terrorist acts and false surrenders.

The detainees are former Taliban fighters and others from 42 nations, thought at the time of their capture by the U.S. government to have connections to al Qaeda, the terrorist organization led by Osama bin Laden. In most instances, they were picked up in Afghanistan and Pakistan.

After lengthy interrogation, many of the detainees are thought to be low-level former Taliban fighters, unlikely prospects for commission trials. Several are juveniles. More than a dozen Guantanamo detainees will be sent home this week, while an additional 30 or so are to be brought in.

When the detention center in Guantanamo opened in January 2002, Vice President Dick Cheney called the men in custody there and in Afghanistan "the worst of a very bad lot." On a trip to Guantanamo, Secretary of Defense Donald H. Rumsfeld called them "among the most dangerous, best trained, vicious killers on the face of the Earth."

The Bush administration has categorized the detainees brought to Guantanamo Bay as unlawful combatants, not prisoners of war. Prisoners of war must be released after hostilities end, according to international law.

They have no constitutional rights because they are non-U.S. citizens held outside U.S. territory on land leased from Cuba. Legal advocacy groups have gone to court on the detainees' behalf.

Guantanamo Bay isn't the only source of possible defendants for military commission trials.

Major terror suspects in U.S. custody who are held far from Guantanamo Bay at undisclosed locations around the world could be subject to the trials.

So could accused Sept. 11 suspect Zacarias Moussaoui, if the government is unable to work out its problems in his federal court case over the use of classified information. And if President Bush expands the order he signed in November 2001, Iraqis alleged to have committed war crimes could face commissions.

Michael Ratner of the Center for Constitutional Rights deplores the fact that "some of these people have been there 15 months and not had any kind of a tribunal determine whether they were properly picked up."

Others say any criticism should be tempered by the new reality of life in a post-Sept. 11 world.

"Legally, if you're going to question the validity under the Constitution of what the government has done, what they have done is probably all right, but whether it's socially and morally acceptable, certainly it's uncomfortable," former military prosecutor Jeff Ifrah said.

The Pentagon is moving toward decision day. It has issued rules for the tribunals and is considering candidates to head the prosecution and defense sections.

The crimes for which tribunals may now be used, according to the Pentagon, are:

• Willful killing of protected persons
  
• Attacking civilians
  
• Attacking civilian objects
  
• Attacking protected property
  
• Pillaging
  
• Denying quarter
  
• Taking hostages
  
• Deploying poisonous or analogous weapons
  
• Using protected persons and shields
  
• Using protected property as shields
  
• Mutilation or maiming
  
• Use of treachery or perfidy
  
• Improper use of flag of truce
  
• Improper use of protective emblems
  
• Degrading treatment of a dead body
  
• Rape
  
• Hijacking or hazarding a vessel or aircraft
  
• Terrorism
  
• Murder by an unprivileged belligerent
  
• Destruction of property by an unprivileged belligerent
  
• Aiding the enemy
  
• Spying
  
• Perjury or false testimony
  
• Obstruction of justice related to military commissions