President Barack Obama on Thursday will discuss his plan for closing the U.S. military prison at Guantanamo Bay, Cuba, in an effort to stop a revolt by lawmakers concerned that some of the detainees could be set free in the United States.

Obama will attempt to address concerns about his Guantanamo policy with a speech at the National Archives. Standing in the building that houses the U.S. Constitution and the Bill of Rights, the president will talk about the importance of upholding American values in times of war.

Here are some facts about the prison camp at the U.S. naval base in Cuba.

WHY WAS IT SET UP?

* The detention camp was set up to hold foreigners captured after U.S.-led forces invaded Afghanistan to root out al Qaeda and its Taliban protectors in response to the attacks of September 11, 2001, that killed nearly 3,000 people in New York, Washington and Pennsylvania.

* The United States holds 240 prisoners at Guantanamo and has released or transferred to other governments about 530 other men and teenagers previously held there. Two were released by the Obama administration and the rest by the Bush administration.

* Charges are pending against 21 Guantanamo prisoners, though Susan Crawford, the Pentagon appointee overseeing the Guantanamo trials, has only referred 14 cases to trial. Judges have issued orders freezing the proceedings in six of those.

MOVES TO CLOSE GUANTANAMO

* Bush administration officials repeatedly said they wanted to close the controversial prison, but never advanced a plan to do so. They concluded in 2008 that closure would require legislation that was too difficult to negotiate in a heated election season.

* Shortly after taking office, Obama ordered the closing of Guantanamo. He set a one-year deadline for shutting the prison, barred harsh treatment of terrorism suspects held there and closed secret CIA jails overseas.

* The president's fellow Democrats in the U.S. Senate moved on Tuesday to cut $80 million earmarked for closing the prison camp amid reports the administration was considering moving some of the detainees to the United States and criticism it had no plan for dealing with the prisoners.

WHAT TO DO WITH THE PRISONERS?

* Three prosecutions have been completed in the Guantanamo tribunal system formally known as military commissions -- one defendant pleaded guilty, one was convicted in a contested trial and one was convicted after putting up no defense. The tribunals were authorized after the September 11 attacks to try non-U.S. citizens on terrorism charges outside the regular civilian and military courts.

* Obama's order to close Guantanamo kicked off a review process to deal with relocating, releasing or prosecuting the remaining detainees.

* Obama ordered Guantanamo prosecutors to seek 120-day delays in all pending cases to give his administration time to decide whether to scrap the widely criticized tribunals created by the Bush administration to try suspected terrorists outside the regular U.S. court system. He angered supporters last Friday by reviving the military commission system with some rule changes to better protect the rights of the accused.

(Reporting by Jane Sutton in Miami, David Cutler in London and David Alexander in Washington)

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