US Army prosecutors said Thursday that Private Bradley Manning "abused our trust" and should face a court-martial for one of the most serious intelligence breaches in US history.

Defense attorneys argued meanwhile at the conclusion of a seven-day hearing that the charges against the 24-year-old soldier from Oklahoma accused of spilling secrets to WikiLeaks should be reduced.

Manning, who served in Iraq from November 2009 until his arrest the following May, was "trained and trusted to use multiple intelligence systems," US Army Captain Ashden Fein said in his closing argument.

"He used that training to defy that trust," Fein told the US Army officer who is to decide whether Manning should face a court-martial. "He abused our trust and mined as much possible.

"Ultimately he aided the enemies of the United States by indirectly giving them intelligence through WikiLeaks," pulling more than 700,000 documents from secure networks and providing them to the site, Fein said.

Fein at one point showed snippets of instant message conversations he said were between Manning and WikiLeaks founder Julian Assange and a video during which a member of Al-Qaeda is seen discussing one of the 260,000 State Department cables Manning is alleged to have provided to WikiLeaks.

During six days of testimony, US Army computer experts testified that contact information for Assange, online chats with the WikiLeaks founder, and a trail of other incriminating digital footprints was found on computers used by Manning.

In his closing statement, Manning's civilian defense attorney, David Coombs, urged the presiding officer, Lieutenant Colonel Paul Almanza, to reduce the charges to jut three counts that would carry a total of 30 years in prison.

"The government overcharged in this case," Coombs said, in order "to strong-arm a plea from my client."

Manning faces life in prison if convicted of aiding the enemy, the most serious of the 22 charges he is facing.

Coombs said the charges initially filed against Manning carried a maximum punishment of 150 years in prison but "the government wasn't satisfied, instead they've also charged my client with aiding the enemy."

Charges such as using unauthorized software or bypassing security should be dropped because Manning was serving in a "lawless unit" where soldiers routinely violated regulations by listening to music, watching movies or playing video games on official computers, Coombs argued.

Coombs also urged Almanza to consider Manning's personal problems, saying he was suffering from "gender identity disorder" and had created an online female alter ego called "Breanna Manning."

"He struggled in isolation but he did not struggle in silence," Coombs said, quoting from an anguished letter the soldier wrote to a sergeant in his unit, Paul Adkins.

"It's haunting me more and more as I get older," Manning said of his gender struggles, adding that they were making his "entire life feel like a bad dream that won't end."

"That's the letter the sergeant first class received and he did nothing," Coombs said. "The military's lack of response smacks of injustice."

The defense has also suggested that Manning, who is gay, had difficulty serving in a US military that was operating under "Don't Ask, Don't Tell," a policy towards homosexuals which has since been repealed.

The US government has said the biggest leak of classified US material since Daniel Ellsberg turned the Pentagon Papers over to The New York Times in 1971 endangered sources and damaged US national security and foreign relations.

But Coombs dismissed the government's claims. "The simple fact is that it hasn't caused harm," he said. "If anything it has helped."

Coombs described Manning as someone who was "young and idealistic" with a "strong moral compass."

"History will ultimately judge my client," he said.

Dressed in a green camouflage uniform of the 10th Mountain Division, Manning listened intently and whispered something into his attorney's ear at the end of his 20-minute closing argument.

The presiding officer is not expected to make a decision on whether or not to proceed to a court-martial for several weeks. He has until January 16 to make a decision but can request a delay.

Ellsberg, the Pentagon Papers whistleblower, was among Manning's supporters who have attended the hearing at Fort Meade and his backers have held several vigils and rallies outside the army base.