United States prosecutors will seek a minimum 20-year jail term for terror suspect David Hicks, his defence team said yesterday.

Hicks's Australian lawyer, Michael Griffin, said that during a recent meeting with officials in the United States to discuss his client's case the chief prosecutor, Colonel Mo Davis, said he would seek a 20-year sentence for Hicks.

"[Colonel Davis] was of the view that nothing less than 20 years would be appropriate and taking into consideration the time served, although not necessarily on a day-for-day basis, a sentence of at least 15 years would be sought, after any discount," Mr Griffin said.

He said Colonel Davis's deputy and a senior Justice Department official were also present.

Mr Griffin said the news "added to David's despair".

"His condition was not good and it added to his obvious distress. It's unfortunate we had to contribute to this distress by appraising him of these unpleasant factors," he said.

Colonel Davis was not available for comment yesterday.

The news came as US officials said Hicks would be returned to Australia if acquitted, but that other Guantanamo Bay detainees could be kept in detention even if found not guilty.

As hundreds of protesters gathered in Canberra yesterday to demand that Hicks be brought home, Prime Minister John Howard conceded there had been a shift in community sentiment over his detention.

Liberal and Nationals MPs and senators made it clear to Mr Howard during a party-room meeting that Hicks' treatment was becoming a significant issue in the electorate.

MPs Bruce Baird, Petro Georgiou and Warren Entsch called for Hicks's return.

Speaking yesterday to reporters in Canberra via a video link, legal adviser to the Secretary of State, John Bellinger, and deputy in the office of war crimes issues at the US State Department, Sandra Hodgkinson, said the 395 detainees at Guantanamo were being held as combatants in a war and therefore the US was under no obligation to charge them. "Let me be clear, we do not believe the individuals in Guantanamo have to be charged with crimes in order to be held ... The individuals captured and detained in Afghanistan or Pakistan were detained not because they were criminals ... they were detained by our soldiers or turned over to our soldiers and are being held either because they are in combat with us or because they were members of the Taliban or al Qaeda," Mr Bellinger said.

Ms Hodgkinson said the authority to detain the men was consistent with the laws of war and "therefore they could be detained following their actual acquittal".

However, Mr Bellinger said the Australian Government had been "assured" Mr Hicks would be returned if acquitted.

The officials said it would be "several weeks to more than a month" before the Convening Authority reviewed the charges against Mr Hicks.

The authority must approve the charges before they can be formally served on Mr Hicks.

Once served, the commission must be constituted within 120 days or the case is dismissed.

The officials said between 40 and 80 detainees would eventually be charged. The chief prosecutor, Colonel Davis, has previously told The Canberra Times he anticipated charging a total of 75.

The remainder will be released or detained for the duration of hostilities.

When asked when that might be, Mr Bellinger said he didn't know but said it would "probably ... go on for much longer than a traditional war".

The officials said if Hicks were found guilty he should be able to serve out any prison sentence in Australia.

They rejected claims by Hicks's legal team that their client was to be charged under retrospective laws, saying they were "merely a codification by our congress in the military commissions act of offences that are triable by military commission under the laws of war".

Mr Bellinger said it was "distressing" that Guantanamo Bay had become a "lightning rod" for criticisms of the United States' human rights record.

"I think critics have seen the pictures of Abu Ghraib, they hear statements made about what allegedly happened at Guantanamo and they assume terrible things have happened," he said. "Obviously, there have been some instances of misconduct ... but after numerous investigations those have been relatively few."

The officials also defended the use of evidence obtained through hearsay or coercion, saying witnesses were "scattered across the world", meaning they could not always be present in court.

Mr Bellinger said international courts such as the International Criminal Court and United Nations tribunals also allowed hearsay evidence.

Hicks's Australian lawyer, David McLeod, queried the State Department's assertion that the laws used to try his client were not being applied retrospectively: "... why wasn't Hicks charged with this offence five years ago and put before a Federal court?"

Hicks has been detained in Guantanamo since 2001 after being captured in Afghanistan. Last Saturday charges of attempted murder and providing material support to a terrorist organisation were sworn against him.