LONDON — With the arrest in London of the WikiLeaks founder Julian Assange, and the news of a criminal case against him in the United States, anyone expecting him to appear in an American courtroom should be warned: Extraditing him will not be quick, and it will not be easy.

The American authorities made a preliminary extradition request on Thursday, soon after Mr. Assange was jailed for jumping bail, but that was just the first in a long series of legal filings, hearings, appeals and administrative decisions. And in the end, experts say, the result is far from certain.

The process is mostly up to the courts, but politicians will have a hand in it, too, and were already drawing battle lines over Mr. Assange. Complicating matters, prosecutors in Sweden could reopen a rape investigation involving Mr. Assange and request extradition to that country, forcing the British government to decide which case would take precedence.

“It’s not simple, and the defense will argue everything they can,” said Rebecca Niblock, a partner at the British law firm Kingsley Napley who specializes in extradition law. “I think it is going to be a long one. I’d say minimum a year and a half, but if things get complicated, it could be much longer.”