The date for a full hearing was set by Westminster Magistrates Court on Friday after Home Secretary Sajid Javid agreed to the American request.
The 47-year-old Wikileaks founder, who is serving a 50-week prison sentence after being dragged out of the Ecuadorian embassy in April and jailed for a bail violation, is fighting against being sent to the US.
The 18 charges levelled against Assange include allegations of conspiring to hack into a classified Pentagon computer.
An investigation has also been reopened into an allegation of rape in Sweden, which Assange has always denied.
Chief magistrate Emma Arbuthnot ordered for a full extradition hearing expected to last five days to begin on 25 February.
Opening the proceedings, Ben Brandon, representing the US, said: “This is related to one of the largest compromises of confidential information in the history of the United States.”
Evidence will show that Assange “first encouraged” former US army intelligence analyst Chelsea Manning to illegally obtain documents, Mr Brandon alleged.
Then Assange agreed with her to “crack” a password hash on a Pentagon computer, the lawyer continued.
“By taking steps to crack the password hash, it’s said that Mr Assange was also attempting to illegally obtain and receive classified information,” Mr Brandon said.
The documents relate to the Iraq and Afghanistan wars and, the lawyer alleged, information on secret intelligence sources.
“By publishing that unredacted material on the internet, Mr Assange created a grave and imminent risk that human intelligence sources, including journalists, human rights defenders and political activists, would suffer serious physical harm or arbitrary detention,” Mr Brandon said.
Appearing by videolink from Belmarsh Prison for the short hearing, Assange, with a scraggly white beard and wearing a grey T-shirt and black-framed glasses, told the court that “175 years of my life is effectively at stake.”
Addressing the judge as Lady Arbuthnot, he defended his website against hacking claims, saying: “WikiLeaks is nothing but a publisher.”
The court also heard that he has a date at the Court of Appeal, with his legal team later explaining he is to appeal against his sentence for breach of bail.
Mark Summers QC, representing Assange, told the court there are a “multiplicity of profound issues” with the extradition case.
“We say it represents an outrageous and full-frontal assault on journalistic rights,” he said.
Protesters outside the court held up banners of support, including one with the message “Free Assange”, while some chanted “justice for Julian Assange” and “defend freedom and democracy”.