Britain’s highest court ruled on Wednesday that theWikiLeaks founder, Julian Assange, should be deported to Sweden to face allegations of sexual abuse there, but Mr. Assange’s lawyers won an immediate stay of at least two weeks before British officials can initiate the final steps to hand him over to Stockholm.

In what had been billed as the culmination of an 18-month legal battle, the Supreme Court ruled by a 5-to-2 vote to reject Mr. Assange’s argument against extradition. The decision was delivered in a court hearing lasting barely 10 minutes by Nicholas Phillips, the 74-year-old president of the court, in one of his last major decisions before retirement this fall.

The ruling turned on whether the Swedish prosecutor who made the extradition request was a competent “judicial authority” under the terms of the European extradition treaty. Judge Phillips, who voted with the majority, said the question “has not been easy to resolve,” but the court majority’s finding that the Swedish prosecutor was a competent authority made the extradition request lawful.
Mr. Assange, who was delayed by heavy traffic, was not present for the decision, but there was an audible sigh of disappointment from WikiLeaks supporters in the courtroom as the ruling was read. That anxiety appeared to relent somewhat as Dinah Rose, one of Mr. Assange’s lawyers, rose to request a two-week delay in implementation of the decision, saying the court appeared to have made its ruling on a fine point of European law that had not been raised by either side at an earlier Supreme Court hearing on the case.
In granting that request and agreeing to consider a new submission from Mr. Assange’s lawyers, the court effectively opened, at least for now, a fresh opportunity for Mr. Assange to delay — and what legal experts said was a narrow and improbable chance to avoid — his forcible removal to Sweden for at least several weeks.
The delay in settling the extradition case in Britain appeared likely to put back indefinitely any moves the United States may have in hand to open a new round of extradition hearings to transport Mr. Assange to the United States to face charges for his role in overseeing the release by WikiLeaks over the last two years of hundreds of thousands of secret American military and diplomatic cables.
There have been frequent but unconfirmed reports for much of that time that a grand jury in Alexandria, Va., has been considering a Justice Department bid to charge Mr. Assange with espionage. Leaked e-mails from the global intelligence company Stratfor earlier this year suggested that a sealed indictment was ready to be made public when American officials judge that legal proceedings against Mr. Assange in Britain and Sweden are coming to a close.
For now, the British case will continue. Gareth Peirce, one of Mr. Assange’s lawyers, said after the hearing on Wednesday that once the Supreme Court had considered the new argument, his lawyers would have seven days to formulate an appeal to the European Court of Human Rights in Strasbourg, France. At that point, legal experts said, only a stay from the European court, which is considered unlikely but not impossible, would prevent Mr. Assange from being extradited. If the European court rejected a new hearing, Mr. Assange would probably be on plane to Stockholm within days, the experts said.
Ms. Peirce said outside court that the Assange legal team would “put in a written submission on the fact that the majority of judges have decided on a basis that was never argued in court by anyone,” referring to the citation the judges made of the interpretation of the words “judicial authority” in the Vienna Convention.
Barely 12 hours before the Supreme Court’s ruling, WikiLeaks issued a statement asserting that Mr. Assange could face moves by the United States to extradite him on espionage charges from Britain, Sweden or Mr. Assange’s native Australia, depending on his whereabouts.
“WikiLeaks is under serious threat,” the WikiLeaks statement said. “The U.S., U.K., Swedish and Australian governments are engaging in a coordinated effort to extradite its editor in chief, Julian Assange, to the United States to face espionage charges for journalistic activities.”

The statement cited reports that the Obama administration has obtained a sealed indictment charging Mr. Assange with espionage, as well as a range of other activities that WikiLeaks said pointed to plans to move against Mr. Assange as soon as the British court proceedings were completed.
It said the preparations included special task forces at the Pentagon, the Central Intelligence Agency, the Federal Bureau of Investigation and the State Department, and secret subpoenas it said had been served on Google, Twitter and other online services to obtain the “private data” of WikiLeaks’s staff members and supporters. 

In effect, the four-page WikiLeaks statement depicted the decision in London as a prelude to a much grimmer challenge awaiting Mr. Assange than the sex abuse charges. Lawyers in Sweden have said he will probably face a stiff fine or at most a brief prison term if he is convicted on the Swedish charges.
But extradition to the United States — involving what would almost certainly be another lengthy legal battle — could put him in jeopardy of a much harsher punishment. If found guilty on espionage charges, he could face a life sentence in a maximum-security prison.
The WikiLeaks document was speculative, since the Obama administration has never said how it plans to act once a final British ruling is handed down. The United States ambassador to Britain, Louis B. Susman, has said the Justice Department will “wait to see how things work out in the British courts,” and there have been reports in the past year of confidential meetings between American officials and representatives of Britain, Sweden and Australia concerning the Assange case.
Mr. Assange has repeatedly said he regards the Swedish sex allegations as a prelude to an American attempt to extradite him to the United States, and has expressed anxiety about his options of finding sanctuary elsewhere in the world where he would be beyond the reach of American law even if he were cleared of the charges in Sweden.
That fear found expression in the WikiLeaks statement. It said Mr. Assange had been unable “to take steps” to avoid extradition to the United States — a phrase that appeared to mean that he could not leave Britain to seek a safe haven elsewhere because he had been detained for over 500 days under what amounted to house arrest in Britain.
The British Supreme Court took nearly four months to consider Mr. Assange’s final appeal, the latest in a string of high-profile actions he has taken to avoid being returned to Sweden, where two former WikiLeaks volunteers accuse him of “four offenses of unlawful coercion and sexual misconduct including rape,” according to the court’s account.
The charges refer to incidents that occurred over 10 days during August 2010, when Mr. Assange, then in the midst of releasing hundreds of thousands of classified United States military and diplomatic documents, had sexual relations in Sweden, as he has acknowledged, with the two women. They subsequently made complaints suggesting that what began as consensual encounters turned non-consensual, allegations Mr. Assange has denied.
Mr. Assange appeared for an initial interview with the Stockholm police shortly after the allegations were made, but fled to London before further questioning could be completed, a court here was subsequently told. He was briefly jailed in December 2010 when Swedish authorities issued a European arrest warrant for his return. He has since been under tight bail conditions that have included a curfew, travel restrictions, regular reports to the local police and electronic tagging.
The activist and hacker, who will turn 41 in July, has always maintained his innocence and has railed at the allegations with characteristic defiance in a series of interviews and messages on Twitter. Sweden, he has said, is the “Saudi Arabia of feminism,” and his lawyers have spoken darkly of a “honey trap,” perhaps intended to thwart Mr. Assange’s ambition to leak further government documents.
WikiLeaks has not released any significant material for more than a year, since a spate of defections weakened its submission and processing systems, and action taken under American government pressure by American credit card and online payment companies effectively starved WikiLeaks of what had been a global flow of donations.
The cumulative effect of his entanglement with the Swedish case, the financial problems facing WikiLeaks and his own difficulty in paying hundreds of thousands of dollars in legal fees have combined with a spate of defections by disillusioned activists to isolate Mr. Assange.
A left-winger since his youth, he has effectively abandoned WikiLeaks’s original pledge to act as a secure, nonpartisan drop box for documents and information from whistle-blowers eager to expose wrongdoing in governments and corporations, and has embraced a wide range of controversial political causes.
One of his recent moves was to accept a position as a talk show host on the international Russia Today television network, which is financed by the Russian government. His first guest was the Lebanese-based Hezbollah leader Hassan Nasrallah.