Bradley Manning, the US soldier accused of having been the source of the massive WikiLeaks dump of state secrets, is one step closer towards the possibility of spending the rest of his life in military confinement after the officer who presided over his pre-trial hearing recommended he be sent to a full court martial.

Colonel Paul Almanza, the investigating officer at last month's hearing in Fort Meade, Maryland, has written to his superiors recommending that all 22 charges against Manning be referred to a general court martial – the most serious military trial. An announcement from the military district of Washington said that Almanza had found that "reasonable grounds exist to believe that the accused committed the offenses alleged."

A final decision will be made by colonel Carl Coffman of the special court martial convening authority, though he has the option of passing it further up the chain of command to major general Michael Linnington.

The outcome of the pre-trial hearing means that a full military trial is almost certain to follow, and is likely to be held within the next three to four months. That will set the scene for what promises to be a dramatic clash of wills between the Obama administration and the military high command on the one hand, and Bradley Manning and his forceful defence lawyer David Coombs on the other.

The administration and the military leadership have made it clear they wish to see a stiff sentence meted out to the soldier as deterrence for any future leaking of state secrets. Manning is charged with aiding the enemy, making intelligence available to the enemy on the internet, theft of public records, computer fraud and violation of military information security.

Manning and Coombs have already indicated that they plan a robust defence. They have raised the relatively harmless nature of the WikiLeaks documents, the army's incompetence, lack of security at the forward operating base outside Baghdad where Manning was working as an intelligence analyst, and neglect towards Manning from his supervisors as possible mitigating arguments.

Jeff Patterson of the Bradley Manning support network said he was disappointed by the move towards a court martial – though "far from surprised. I sat in that courtroom and watched a Department of Justice employee pretending to be an impartial judge."

Patterson was referring to Almanza's civilian job as a Department of Justice prosecutor which Coombs challenged at the pre-trial hearing on grounds of conflict of interest.

Coombs told Almanza on the first day of the hearing that he should recuse himself, because the justice department was pursuing an aggressive prosecution of WikiLeaks and Julian Assange that would inevitably involve Manning as a key witness.

Patterson also objected to the way that the investigating officer at the pre-trial hearing had allowed the prosecution to present all its desired witnesses, but had barred all but a few requested by the defence.

It is understood that a general court martial will take between 90 and 120 days to be convened, after a final decision – expected over the next few days – is announced. At that point Manning and his lawyer will have another opportunity to press for their witnesses to be heard.

Coombs has already begun to press for more disclosure. On the same day as the investigating officer's recommendation was released, Coombs filed a new deposition request with the government.

The defence wants to be able to quiz six military officials in out-of-court testimony about the classification of videos and documents that were part of the trove of hundreds of thousands leaked to WikiLeaks. Almanza previously declined to allow them to be called at the pre-trial hearing, ruling that they were "not reasonably available".