Bradley Manning has pleaded guilty to having been the source of the massive WikiLeaks dump of US state secrets, though he has denied the most serious charge against him that he "aided the enemy" that could see him languishing in military prison for the rest of his life.

Through his lawyer, David Coombs, the soldier pleaded guilty to 10 lesser charges that included possessing and wilfully communicating to an unauthorised person all the main elements of the WikiLeaks disclosure. That covered the so-called "collateral murder" video of an Apache helicopter attack in Iraq; some US diplomatic cables including one of the early WikiLeaks publications the Reykjavik cable; portions of the Iraq and Afghanistan warlogs, some of the files on detainees in Guantanamo; and two intelligence memos.

These lesser charges each carry a two-year maximum sentence, committing Manning to a possible upper limit of 20 years in prison.

Manning also pleaded not guilty to 12 counts which relate to the major offences of which he is accused by the US government. Specifically, he pleaded not guilty to "aiding the enemy" – the idea that he knowingly gave help to al-Qaida and in a separate count that by causing secret intelligence to be published on the internet he knowingly made it accessible to the enemy.

He also denied that at the time he made the transmission of information to WikiLeaks he had "reason to believe such information could be used to the injury of the United States or to the advantage of any foreign nation".

With Manning having pleaded not guilty to these overarching charges, the prosecution is now almost certain to press ahead to a full court-martial which is currently set for 3 June. The judge has indicated that the trial could run for 12 weeks, although Manning's guilty plea to the lesser charges may short-circuit the process as the government will no longer have to prove that he acquired and communicated the trove of classified material to WikiLeaks.

Manning confirmed that he wishes the trial to be conducted by the judge, Colonel Denise Lind, presiding in the case sitting alone. There will be no military equivalent of a jury.

Lind made clear that she will reserve her judgment on whether or not to accept Manning's guilty pleas until a later date. She has no power to influence the charges other than to ensure that they are consistent with the law – which she has already done.

She does, however, have the responsibility to ensure that Manning has made his plea in full knowledge of what it means for his future, and voluntarily with no coercion.

They will now spend the rest of the day in deliberations designed to meet that responsibility. Lind has said that Manning will be allowed to read out a statement, believed to run to 35 pages, that explains his decisions and may reveal his thinking about what he did and why he did it in transmitting such a huge mountain of classified material to WikiLeaks.

Live tweets from Ed Pilkington at Fort Meade