A Swedish teen-ager who paralyzed American telephone switchboards for months, prompting a global hunt by the Federal Bureau of Investigation, was fined the equivalent of $350 by a Swedish court today.

The self-styled ''Demon Freaker,'' who was not named in court, jammed Florida switchboards last year by linking them to sex lines. Then 19, he had cracked the codes of a company that enables Americans to call home from abroad, allowing him to call anywhere in the United States free.

Working from his bedroom at night in this western Swedish city, he made 60,000 calls, ringing up $250,000 in phone bills at the American company's cost. He managed to transfer the number of the magazine Hustler to his own line so that he received orders for the magazine and for sexual paraphernalia.

The F.B.I. picked up the teen-ager's trace in February 1996, when he placed a crank call to an American emergency number.