LONDON — Lawyers acting for Julian Assange, the founder of the WikiLeaks antisecrecy group, said on Tuesday they would argue against a demand for his extradition to Sweden on the grounds that he might subsequently face “illegal rendition” to the United States, risking imprisonment at Guantánamo Bay, or even the death penalty.
The assertion came in defense documents released after Mr. Assange made a brief appearance in a British high-security court for a largely procedural hearing concerning his resistance to Swedish demands for his extradition following allegations of sexual misconduct.
The documents also for the first time publicly named the two WikiLeaks’s volunteers who alleged that Mr. Assange forced sex on them without using a condom in Sweden last August, in one case while the woman, according to her account, was asleep. In keeping with Sweden’s policy of anonymity for those involved with rape cases, they had previously only been referred to as Ms. A and Ms. W.
Karin Rosander, a spokeswoman for the Swedish prosecutors’ office, could not immediately say whether the disclosure constituted a crime, but said it was possible under certain circumstances and that investigations would take place. Jennifer Robinson, one of Mr. Assange’s London lawyers, said that the inclusion of the women’s names in the defense documents was an oversight that would be corrected.
The court hearing set the date for the extradition hearing as Feb. 7 and 8. The sexual accusations, which Mr. Assange denies, have overlapped with WikiLeaks’s publication of about 2,000 State Department documents from a trove of some 250,000 in its possession, exposing confidential or secret communications to broad public scrutiny on its Web site and in newspapers including The New York Times along with The Guardian, Der Spiegel, Le Monde and El País.
“Our work with WikiLeaks continues unabated and we are stepping up our publishing for matters relating to Cablegate and other materials,” Mr. Assange said after Tuesday’s 10-minute hearing, using the organization’s term for State Department documents. “Those will shortly be appearing through our newspaper partners throughout the world,” he said, without elaborating on the content of the threatened disclosures. In recent weeks the flow of new documents has slowed to a trickle.
Mr. Assange was jailed in Britain in early December after a Swedish prosecutor issued a European arrest warrant seeking his extradition to be questioned about the sexual accusations. He was released on $370,000 bail nine days later, on Dec. 16.
In a 35-page outline of their case against extradition, released on the WikiLeaks Web site, Mr. Assange’s lawyers said: “It is submitted that there is a real risk that, if extradited to Sweden, the United States will seek his extradition and/or illegal rendition to the U.S.A., where there will be a real risk of him being detained at Guantánamo Bay or elsewhere.”
“Indeed if Mr. Assange were rendered to the U.S.A. without assurances that the death penalty would not be carried out, there is a real risk that he could be made subject to the death penalty.” The document cited statements by senior American politicians calling for the execution of those who leaked the State Department documents.
Mr. Assange’s lawyers released the outline of the defense case within minutes of Tuesday’s court hearing, saying they would also argue that Swedish law did not permit their client to be extradited on “the mere suspicion” that he had committed offenses. The lawyers argued that Swedish prosecutors had said publicly they were seeking his extradition solely to question him about the accusations of sexual misconduct.
The defense also said Mr. Assange had been “the victim of a pattern of illegal or corrupt behavior” by Swedish prosecutors who were alleged to have made a series of procedural and other errors in their handling of the case.
Previous hearings in the case have been held in central London courts. But the hearing on Tuesday was set for the Belmarsh high-security court in the southeast of the city, which is more usually associated with terrorism cases. Britain’s court service said the move was designed to accommodate reporters and camera crews who had scrimmaged for position outside and inside the other courts.
Wearing a gray duffle coat over a dark suit and tie, Mr. Assange arrived with his British lawyer, Mark Stephens. Once in court, he made thumbs-up gestures toward associates in the public gallery and seemed relaxed.
The WikiLeaks disclosures have incensed officials in Washington, including Secretary of State Hillary Rodham Clinton. American Justice Department officials are seeking to determine whether they can bring charges against him.
Prosecutors have gone to court to demand records of the Twitter account activity of several people linked to WikiLeaks, including Mr. Assange, according to the group and a copy of a subpoena made public late last Friday.
The subpoena is the first public evidence of a criminal investigation, announced last month by Attorney General Eric H. Holder Jr., that has been urged on by members of Congress of both parties but is fraught with legal and political difficulties for the Obama administration.
It was denounced by WikiLeaks, which has so far made public only about 1 percent of the quarter-million diplomatic cables in its possession but has threatened to post them all on the Web if criminal charges are brought.
For some of Mr. Assange’s supporters the secrecy issues have become conflated with the court hearings in London since he was arrested last month.
When Mr. Assange, a 39-year-old Australian, was released from jail last month, his bail conditions require him to stay in Ellingham Hall, a luxurious mansion on a 650-acre estate in eastern England, wear an electronic tag and report to local police officers every day. He has described the conditions as “hi-tech house arrest.”
During his stay there, he has signed deals to publish an autobiography that, he told a British newspaper, might be worth $1.7 million.
On Tuesday, the court agreed for him to move to central London for two days during the full extradition hearing next month. He will be staying at the Frontline Club, founded by Vaughan Smith, the owner of Ellingham Hall.
Ravi Somaiya reported from London, and Alan Cowell from Paris.