The U.S. Department of Justice will undertake a full priority probe into last year's shooting deaths of two youths who favored independence for Puerto Rico to determine whether they were entrapped by police on a deserted mountaintop in the interior.

U.S. Attorney Julio Morales Sanchez said today that the department's civil rights decision gave him the go-ahead to expand a preliminary investigation he began in January before a federal grand jury here.

Anti-independence Gov. Carlos Romero Barcelo recently admitted having general knowledge that the two alleged terrorists were going to attack communications towers in Villalba, after previously denying any knowledge of the scheme. The admission, which Morales Sanchez said did not motivate the department's decision, has heightened charges of "cover-up" from the governor's political foes. These charges apparently were the reason Romero Barcelo went on the air Thursday evening to discuss the case.

The youths, accompanied by a police double agent, were fired on by four police officials not in uniform while allegedly trying to blow up the two communications facilities.

The towers are concrete and steel, hundreds of feet high. The youths were carrying handguns, turpentine, charcoal and a box of matches.

The Justice Department is expected to explore whether the police acted "improperly and used excessive force."

Other questions the Puerto Rican media have vociferously raised are whether the youths were entrapped by the police into their attack on the towers, who shot first, and why one of the dead youths arrived at a hospital with bruises on face and body.

The FBI is expected to be called in to gather evidence. The grand jury meets again in June, and the investigation should be in full force in a week.

Morales Sanchez declined to say who will be called to testify, but sources said the list will include all persons with "first-hand" knowledge of what has become a politically charged event. Among them will be the undercover agent, Alejandro Gonzalez Malave, police superintendent Desiderio Cartagena and former police chief Roberto Torres Gonzalez. The governor is not likely to be called, the sources said.

The incident, involving Arnaldo Dario Rosado, 23, and Carlos Soto Arrivi, 18, son of a prominent Puerto Rican novelist, first evoked sharp controversy when the governor praised the police for a "heroic" shootout effort.

Months later a Puerto Rican Department of Justice probe exonerated police of any wrongdoing, saying they acted in self-defense. The undercover agent was slightly wounded in a finger in the shootout.

The agent said in a sworn statement that the two youths were members of the Armed Revolutionary Movement which he infiltrated more than a year before the July 25 incident. He said the group was determined to pull off some kind of attack to protest Constitution Day celebrations. But Julio Ortiz Molina, a taxi driver who was kidnaped and forced to drive the youths to the Cerro Maravilla area, said in a sworn statement that the undercover agent appeared to be the leader of the group.

Ortiz Molina so far has been the only grand jury witness, and sources say his four-hour testimony at times contradicted the statements of others. He had said that there were more than four policemen on the scene, that he heard a second volley of shots, and that one of the youths was still alive when he last saw him. Both were dead on arrival at the nearby hospital.

The controversy heightened last week during Puerto Rican Senate hearings on the nomination of a new police superintendent. Desiderio Cartagena testified that he did not know whether the governor was informed of the event before it occurred. However, the governor recently acknowledged having been told by Cartagena himself.

The new police chief's testimony will be "evaluated" by the local department of justice to determine whether perjury was committed.