FORT MEADE: US Army Private Bradley Manning will be sentenced Wednesday for handing a mass of data to WikiLeaks in the biggest breach of official secrets in American history.

The 25-year-old soldier was convicted of espionage and other crimes last month, having admitted being the source of hundreds of thousands of war reports from Afghanistan and Iraq and confidential US diplomatic cables.

His sentencing, due at 10 am (1400 GMT), is considered especially important as another leaker, the former intelligence contractor Edward Snowden, currently in Russia, is wanted in the United States on espionage charges, having disclosed details of the National Security Agency's secret electronic monitoring operations.

Military prosecutors on Monday pressed for a 60-year prison term for Manning, arguing that the penalty would send a message to people contemplating the theft of classified information.

Lead defense attorney David Coombs, however, appealed for leniency for his client. He said Manning had expressed remorse, cooperated with the court and deserved a chance to have a family and one day walk free. His youthful idealism contributed to his belief that he could change the way the world viewed the wars in Iraq and Afghanistan, and all future wars, by leaking the secret files, Coombs said. ''He had pure intentions at the time that he committed his offenses,'' Coombs said.

Prosecutors have called Manning an anarchist computer hacker and attention-seeking traitor. The soldier's supporters have hailed Manning as a whistleblower.

Prosecutors have requested a far longer prison term than other soldiers have received in recent decades for sharing government secrets and did not say why they were not seeking the maximum punishment for Manning, who was convicted last month of 20 offenses, including six violations of the Espionage Act and five counts of stealing protected information.

''There's value in deterrence,'' Morrow said.

The defense has suggested a prison term of no more than 25 years, so that Manning, 25, could rebuild his life. Defense attorney David Coombs asked for a sentence that ''doesn't rob him of his youth.''

Army Spec. Albert T. Sombolay got a 34-year-sentence in 1991 for giving a Jordanian intelligence agent information on the buildup for the first Iraq war, plus other documents and samples of US Army chemical protection equipment. Marine Sgt. Clayton Lonetree, the only US Marine ever convicted of espionage, was given a 30-year sentence, later reduced to 15 years, for giving the Soviet KGB the identities of US CIA agents and the floor plans of the embassies in Moscow and Vienna in the early 1980s.

US civilian courts have ordered life in prison for spies, including Aldrich Ames, a former CIA case officer convicted in 1994 of spying for the Soviet Union and Russia and former FBI agent Robert Hanssen, convicted in 2001 of spying for Moscow.

Government transparency advocate Steven Aftergood, of the Federation of American Scientists, said the civilian cases, unlike the military ones, involved career intelligence workers who knowingly supplied foreign governments with US secrets for years. Ames' disclosures caused intelligence sources to be executed. Hanssen compromised ongoing intelligence operations on a massive scale.

The prosecutors' request for 60 years likely reflects their view that Manning's offenses were less egregious than if he had specifically sought out foreign agents and given them information, said Michael Navarre, a former Navy judge advocate. The government was unable to show that Manning knew the documents would get to Al-Qaeda, and Manning has said he only leaked information that he believed would not be harmful. Manning took the stand last week and apologized for hurting his country, pleading with the judge for a chance to go to college and become a productive citizen.

Family members and a psychologist testified for the defense, saying the soldier felt extreme mental pressure in the military because of his gender-identity disorder during the era when openly gay people were not allowed to serve in the military.

Manning was a junior intelligence analyst at a US base near Baghdad when he handed over the data, about 700,000 reports and diplomatic cables, to WikiLeaks, the anti-secrecy website headed by Julian Assange.

Manning was arrested in Iraq in 2010 and has been in military custody since. The documents that he disclosed rankled American allies when WikiLeaks published them, prompting warnings from US officials that troops and intelligence sources had been jeopardized.

The most notorious breach was a video and audio file, dubbed “Collateral Murder” by WikiLeaks, showing graphic cockpit footage of two US Apache attack helicopters opening fire and killing 12 people in Baghdad in 2007.

Manning, a hero to supporters who regard him as a whistleblower who lifted the lid on America's foreign policy, was found guilty of 20 of the 22 charges leveled against him.

He was, however, cleared of the most serious charge, “aiding the enemy,” chiefly Al-Qaeda. More than 100,000 people have signed a petition calling for Manning's nomination for a Nobel Peace Prize.

Underlining the seriousness of the case, the US government painted him as a reckless traitor whose actions put his country at danger.

Manning also apologized. “I'm sorry that my actions have hurt people and have hurt the United States,” he told US military judge Colonel Denise Lind last week.

“I want to go forward. I understand I must pay the price,” Manning said.

Judge Lind has said that Manning will have 1,293 days removed from his eventual sentence, given his time in custody so far plus credit for a period spent in harsh conditions at the US Marines Corps brig at Quantico, Virginia.