A US military judge has said she will announce a sentence Wednesday for Bradley Manning, the soldier convicted of espionage for giving classified government documents to WikiLeaks.

The judge, Colonel Denise Lind, opened proceedings in the court early Tuesday and adjourned within five minutes to begin her deliberations on Manning's punishment over the massive leak.

"I will be ready to announce the sentence tomorrow at 10:00 am," or 1400 GMT, Lind said later in the day.

The bespectacled Manning, 25, clad in his customary dress blue Army uniform, sat silently next to his military and civilian lawyers, listening to the proceedings in a courtroom at Fort Meade, northeast of Washington.

Military prosecutors on Monday demanded a 60-year prison sentence for Manning, saying the penalty would send a message to any soldier contemplating stealing classified information.

Lead defense attorney David Coombs, however, appealed for leniency for his client, saying Manning had expressed remorse, cooperated with the court and deserved a chance to have a family and one day walk free.

Coombs said Manning was young and "naive", but had good intentions when he leaked classified files in hopes of shedding light on US foreign policy.

The judge said Manning would have 1,293 days removed from his sentence, getting credit for his pre-trial confinement after May 2010, which included a nine-month period in harsh conditions at a military jail in Virginia.

The former junior intelligence analyst admitted to handing over about 700,000 classified battlefield reports and diplomatic cables to the anti-secrecy website WikiLeaks.

The documents rankled allies and prompted warnings from US officials that troops and intelligence sources were put at risk.

Manning pleaded guilty to lesser offenses that could result in a 20-year sentence but the judge found him guilty on more serious counts of espionage, theft and computer fraud, which carry a potential 90-year sentence.