GOTEBORG, Sweden (AP) _ Four men faced aggravated arson charges today as most victims' relatives and survivors of a fire that killed 63 youths watched in a room separate from the main proceedings.

The trial was moved to a sprawling exhibition hall divided into three sections to accommodate the 600 survivors and victims' relatives expected to attend. It was likely to last about two weeks.

The chief judge threatened to stop the trial if there were any interruptions.

``This is an unusual trial where the courtroom is divided into different sections, but the same rules apply in all three courtrooms,'' Judge Bengt-Aake Engstroem said as he opened the proceedings.

Shoresh Kaveh, 19, Housein Arsani, 19, Mohammad Mohammadamini, 21, and Meysam Mohammadyeh, 19, all born in Iran but now living in Sweden, quietly looked on as prosecutors and defense attorneys began to outline their case.

All have denied the charge of aggravated arson, though defense attorneys acknowledged at least three defendants were present in the stairwell where the fire started.

The four were arrested earlier this year but formally charged only last week after a team of 15 investigators and two prosecutors eliminated other leads yielded by 1,800 interviews and a reward of up to $337,000 for information helpful to the case.

Conviction for aggravated arson carries a sentence of six years to life in prison, but Swedish law would allow a lesser sentence because the suspects were under age 20 at the time of the fire.

Most of those who attended the 1998 dance at the rented hall in Goteborg, 300 miles southwest of the capital, Stockholm, were immigrants or children of immigrants. The fire killed 63 and injured more than 200.

Authorities suspected arson from the beginning because the fire spread so fast, giving dance-goers little time to escape and forcing the panicked teen-agers to flee down a single, narrow staircase. Many leapt from second-story windows.

Prosecutors said a flammable liquid was poured over chairs stacked in the emergency stairwell and set alight after an argument between the party's organizers and at least some of the defendants over the $5 entrance fee.

The dance was organized by four teen-agers who rented the hall from the cultural Macedonian Association during a holiday week. About 400 people were crammed into a space legally licensed for 150 when the fire broke out.

Victims came from at least 27 different cultural backgrounds and authorities were providing interpreters to translate trial proceedings from Swedish into 13 languages.

The exhibition hall was divided into a main courtroom for the judges, defendants, their relatives and a limited number of survivors; and two rooms where reporters and spectators could watch on closed-circuit TV.

Swedish law gives survivors and victims' relatives the right to put questions to the defendants and claim damages. Some were upset about being separated from the main proceedings, but authorities said they had little choice given the number of victims.