LYSEKIL, Sweden (AP) _ Police picked through burned-out cabins on the ferry Scandinavian Star today, looking for more victims and for the origin of the weekend fire that killed up to 200 people on a trip from Norway to Denmark.

Investigators, working on the theory of arson, said they found no evidence yet of the spark that ignited the 20-year-old Danish ship carrying more than 500 passengers and crew in the North Sea early Saturday.

Police had not inspected all parts of the ship and were painstakingly moving through the hulk searching for clues, said Roar Onso, district police chief in Lysekil on Sweden's southwest coast.

''We are not going over the whole ship to count bodies,'' he said by telephone. ''The work is slow. We are going over one part at a time and finishing that before we move on to the next.''

Norwegian police today took charge of the investigation of the fire, which occurred midway through the overnight voyage from Oslo to Frederikshavn, Denmark.

The ship's owner has said the blaze was deliberately set because it was one of two fires that broke out on separate decks.

Two other ferry fires occurred Monday off the European coast.

A blaze on the Irish Sea car ferry Norrona with 297 aboard killed one man and injured 32, and the ship's Irish owner suspected arson. The French ferry Reine Mathilde had an engine room fire while off Britain's Isle of Wight and one of 675 aboard died of a heart attack. The cause was under investigation.

Police searching the Scandinavian Star have found 140 victims, but estimates of the casualty toll ranged up to 200 after many children were discovered among the dead. Children under 7 are not registered on passenger lists.

Onso said 109 victims were brought ashore. They were being taken to Oslo, Norway for identification.

Officers, shaken by what they had seen, said they found families who died in their cabins with their arms around each other, and parents who threw themselves over their children in a desperate effort to protect them from the poisonous smoke and unendurable heat.

News photographers allowed into lounge areas of the 10,500-ton vessel recorded a devastated scene of black twisted metal, in which nothing combustible remained.

A commission of high-level officials from Norway, Sweden and Denmark was due to start work in Oslo today, and a maritime inquiry was to open Wednesday in Copenhagen, Denmark.

The disaster revived warnings by Scandinavian sailors against what they called the proliferation of ships flying flags of convenience in Nordic waters which come under less strict safety controls.

The Scandinavian Star, bought last month by the Danish-based Da-No Line from SeaEscape of Miami, was registered in the Bahamas. It had been working the Norway-Denmark line for one week.

Portuguese trade unions representing sailors on the Scandinavian Star charged that some Scandinavians were exploiting the incident for a campaign to bar foreign-flagged ships from Nordic routes.