SANTIAGO, Chile (AP) _ A military court reversed a civilian judge Tuesday and accused an army patrol commander of ''unnecessary violence'' in the burning death of a Chilean-born U.S. resident during anti-government demonstrations.

The court rejected the army version that 19-year-old Rodrigo Rojas de Negri, a resident of Washington, D.C., and Carmen Quintana Aranciaba, 18, were burned when she kicked over a can of gasoline while trying to erect a street barricade during the July 2 demonstrations.

Rojas, who had left Chile with his mother 10 years ago, died July 6. Miss Quintana remains hospitalized.

Fourteen witnesses told a civilian judge, Alberto Echavarria, they saw uniformed men douse both victims with a flammable liquid and set them ablaze. But Echavarria accepted the army account. He cleared 24 members of the army patrol of any suspicion but ordered their commander, Lt. Pedro Fernandez Dittus, to stand trial in a military court on criminal negligence charges for failing to seek medical help for the couple.

In its 4-1 ruling, the military court voted to upgrade the indictment to the more serious charge and instructed an army prosecutor to consider indictments against the other patrol members.

The court's air force and national police representatives joined two civilian judges in the majority ruling. The army member dissented. All military courts in Chile have civilian members.

''This is an important turn in the investigation,'' said Luis Salazar, the lawyer representing the Rojas family. ''The court has destroyed and buried the army's version of the truth.

''Our next step is to ask the court to investigate at what level in the army the real story was covered up,'' he said.

Lt. Fernandez now awaits a verdict by the military court. If convicted of the charge of unncecessary violence he could be sentenced to up to 20 years in prison.

There were a series of demonstrations in July against the military government of President Augusto Pinochet.

Pinochet, a general and the commander of the army, came to power in September 1973 in the bloody coup that ousted the elected government of the late Marxist President Salvador Allende.