Hicks is accused of fighting for al-Qaeda in Afghanistan during the US-led invasion in late 2001.
He was originally charged with war crimes and conspiracy to commit murder, but now faces the less specific charge of providing material support for terrorism.
Human rights groups have criticised the tribunal saying the process lacks legal safeguards, while the crime with which Hicks is charged did not even exist when he was captured in 2001.
Plea deal

"I recognize that around the world, 'Guantanamo,' when you say the word, has a negative connotation"

Air Force Colonel Morris Davis,
the chief prosecutor

Appearing before the tribunal for the initial the arraignment part of his trial, Hicks deferred entering a plea.
Earlier his Australian lawyer, David McLeod, said Hicks was convinced he would not get a fair trial and has not ruled a deal to plead guilty if it would get him home sooner.
McLeod said there had been discussions about a potential plea agreement under which Hicks would plead guilty in return for a reduced sentence.
Australia has agreed a deal with the US that would allow Hicks to serve his sentence in Australia if he is convicted.
During Monday's hearing Hicks, wearing a khaki prison jumpsuit, told judge he was satisfied with his Pentagon-appointed attorney but wanted more defence lawyers and paralegals "to get equality with the prosecution."
But instead the judge, Marine Col. Ralph Kohlmann, said two civilian lawyers, including a defence department attorney, were not authorised to represent him.
The two were ordered to leave the defence table when Hicks said he would not settle for them being designated as legal consultants.
One of the lawyers, Joshua Dratel, said he refused to sign an agreement to abide by tribunal rules because he was concerned the provisions do not allow him to meet with his client in private.
Hicks's father, Terry, was allowed to meet
his son before the hearing [EPA]
The US military flew Hicks' father and sister to the base and allowed them to meet privately with him in the court building before the hearing started.
Hicks has previously appeared before an earlier military tribunal system created by a presidential order, which the US supreme court later ruled unconstitutional.
Last year the US congress, then under a Republican majority, passed a law authorising a reconstituted tribunal regime with some adjustments but still operating outside of regular US courts or military courts-martial.
The commission law permits hearsay, evidence obtained through "coercion", to be admitted to the case, and bars detainees from appealing their detention in US courts.
Hicks' lawyers and human rights monitors observing the hearings say the trials are rigged to ensure convictions and allow the information obtained through coercion.
Hicks is not accused of involvement in the September 11 attacks on New York and Washington DC and Human Rights Watch has said he could easily be tried in a regular US court.
Speaking to reporters before Monday's arraignment hearing, Air Force Colonel Morris Davis, the chief prosecutor for the tribunals, said prosecution planned to prove Hicks had provided "support for the al-Qaeda organisation".
Davis admitted critics had effectively turned public opinion against the Guantanamo tribunals but said he expected that to change once the military begins presenting evidence.
"I recognize that around the world, 'Guantanamo,' when you say the word, has a negative connotation," he said.
"One thing I hope is that in the way we conduct these proceedings, maybe we can change some of those attitudes."