The Chilean Army today arrested 25 soldiers, including three officers, in the burnings of a 19-year-old Washington resident and a companion during antigovernment protests on July 2.

The Washington youth, Rodrigo Rojas, died four days later in a Santiago clinic. The second victim, Carmen Quintana, 18, is still hospitalized.

The commander of the Santiago garrison, Brig. Gen. Carlos Ojeda Vargas, said at a press conference tonight that three officers, five noncommissioned officers and 17 conscripts had been "put at the disposal" of Judge Alberto Echavarria, who was named by the courts to investigate the case following requests for an inquiry from the victims' families and Chile's Interior Ministry.

None of the detainees was named, nor were their ranks revealed.

The Army first denied involvement in the incident, in which witnesses and human rights activists said a military patrol beat Rojas and Quintana before soaking them with a flammable liquid and setting them afire. Ojeda said tonight, however, that "later inquiries allowed it to be deduced that certain Army personnel were involved."

Ojeda did not take questions from reporters.

The general's statement contradicted witnesses' accounts that the troops deliberately burned the couple. Instead, Ojeda said, a military patrol, deployed to "safeguard public order" at the beginning of the two-day general strike, "had surprised a group of people intent on creating disturbances and who carried inflammable material in containers for this purpose."

According to the Army statement, one of these containers overturned, "as the result of actions by one of the detainees," and set the two young people's clothes afire. The soldiers then put out the blaze with blankets, the Army said.

Witnesses and lawyers for the victims' families have said that Rojas and Quintana later were found wandering alone on a deserted road on another side of the city. They also have alleged that the two were loaded onto a pickup truck by soldiers, who sat on them as they were driven away from the scene of the incident.

Rojas was visiting Santiago for the first time after 10 years in exile in Washington with his mother, former political detainee Veronica de Negri.

De Negri, who was allowed to return briefly to Chile after the U.S. Embassy intervened, accused the Chilean government of lying about the circumstances of the attack and charged that authorities had blocked her son's transfer to a hospital where his severe burns could be treated more adequately.

The Chilean Embassy in Washington denied de Negri's allegations. The State Department said last week, however, that embassy personnel had tried for three days to arrange Rojas' transfer.

According to statements to a local radio station by the lawyer for the victims' families, Hector Salazar, today's detentions showed "irresponsibility by the Army high command in declaring within hours of the incident that none of their personnel were involved."

"If the victims were burned as a result of their own actions," Salazar said, "there was no reason why they should not have been taken straight to receive medical attention."

Echavarria, whose selection to head the investigation has aroused controversy, was strongly criticized when he conducted an inquiry five years ago into the murder of a student. Although strong evidence was presented implicating police detectives, the case was suspended without any convictions.

About 20 witnesses have been interviewed by Echavarria in the 10-day-old investigation. Reuter reported the following:

Chile's national Civic Assembly, an alliance of professional, small business and labor groups, announced protests set for next week against the military government of President Augusto Pinochet.

Dr. Ricardo Vacarezza, the Assembly's new coordinator, said the organization would continue to practice civil disobedience by refusing to pay certain debts to the government and boycotting products advertised on what it calls distorted television news.