DAVID Hicks's sentence will be "substantially less" than 20 years in jail, the US military's chief prosecutor said today.

Hicks's sentencing will begin late tonight (Australian time) and both the defence and prosecution have been tight-lipped since Hicks's guilty plea on Monday about what sentence they will recommend.

Chief prosecutor Colonel Morris Davis declined to say today whether a plea deal had been reached with Hicks' defence lawyers, but he gave insight into what Hicks may receive.

John Walker Lindh, dubbed "The American Taliban", was sentenced to 20 years' jail in 2002 and for months Col Davis had used Lindh as a benchmark for Hicks' sentence.

However, Hicks's guilty plea would reduce the sentence prosecutors asked for, Col Davis said.

Asked today about Hicks' potential sentence, Col Davis said the sentence prosecutors will ask for would be much lower than Lindh's 20 years.

"I think you'll find when we get to argument we will argue for something substantially less than John Walker Lindh," Col Davis said at Guantanamo Bay military base.

Hicks's sentencing proceedings are due to begin tomorrow at 8am local time (10pm Friday AEDT).

Hicks, 31, on Monday pleaded guilty to a charge of providing material support for terrorism.