LONDON  Julian Assange, the WikiLeaks founder, must be extradited to Sweden to face accusations of sexual abuse, a British court ordered Thursday. Mr. Assange immediately said he would appeal the decision.

Judge Howard Riddle took just over an hour to issue a sweeping dismissal of the defense team’s arguments  from arcane technical points to dark suggestions that Mr. Assange would not receive a fair trial in Sweden and might even face extradition to the United States, imprisonment at the Guantánamo Bay, Cuba, prison and possibly death.

The judge said that Mr. Assange appeared to have been “deliberately avoiding interrogation” when he left Sweden in September in the wake of allegations by two women in Stockholm that he had sexually abused them. Under Sweden’s strict sexual-crimes laws, he is accused of two counts of sexual molestation, one count of unlawful coercion and one count of rape. His accusers, both WikiLeaks volunteers, have said that their sexual encounters with Mr. Assange started out as consensual but turned nonconsensual.

Under the circumstances, Judge Riddle said, Swedish prosecutors had every right to issue a warrant last December for his arrest and return.