Forensic experts today amended a report on the cause of death of a priest who backed the outlawed union Solidarity, saying he may have been alive when thrown into a reservoir by secret police agents.

But the pathologists from Bialystok, where the body of the Rev. Jerzy Popieluszko, was examined affirmed that the priest did not die from drowning. They blamed the death on a combination of factors, including beating, gagging and strangulation.

The doctors presented their findings at the trial in Torun of four secret police officers charged in the priest's murder. The testimony contained a vaguer version of the time of death than was given in an autopsy report released by the government Nov. 30. Popieluszko was said then to have died before his body was dumped in the Vistula River reservoir at Wloclawek, northwest of Warsaw.

Today's medical statement was more definite, though, than the earlier report about the effect of the blows dealt the frail, 37-year-old priest, citing them as a primary cause of death. The doctors had previously said the death resulted from "suffocation or strangulation," using a Polish word that carries both meanings.

The new conclusion is important because it undercuts the defense of the ringleader of the group that abducted the priest, former captain Grzegorz Piotrowski, who had interpreted the earlier finding to mean his clubbing of Popieluszko was not the cause of death.

As Dr. Tadeusz Jozwik read in court the details of the injuries inflicted on the cleric -- listing at least 14 blows to the head, neck and shoulder -- Piotrowski hid his face in his hands, then sat up silently, his face flushed.

Dr. Maria Byrdy, the pathologist who led the autopsy, said the revised conclusions were due to additional laboratory tests and courtroom testimony by the defendants. She said the earlier report, published a month after the priest's body was found, had been made hurriedly "under strong pressure of public opinion."

Two former police lieutenants accused with Piotrowski of the murder -- Waldemar Chmielewski and Leszek Pekala -- have admitted to gagging and trussing the priest with a rope that was looped around his neck and ran down his back to his ankles, so he would strangle himself if he tried to straighten his knees.

But the two have sought to pin primary responsiblity for the death on Piotrowski who, they said, severely beat Popieluszko on four occasions.

Byrdy avoided singling out any of the accused as chiefly responsible for the killing.

"All these actions -- that is, the blows to the head and the upper part of the body as well as the gagging and the noose -- contributed to the death," she said, adding that the combination of factors led to "a general shock of the system."

But the leading factor, she went on, was probably Popieluszko's choking on blood from head wounds and on vomit brought on by the shock of beatings.

"We cannot say whether he was dead or whether Popieluszko was on the verge of dying when he was thrown into the water," she said. But even if he hadn't been tossed into the reservoir, she added in response to a question, the priest "could not have survived" because after regaining consciousness from the beatings, "he would have moved his legs which would have tightened the noose."

Describing Popieluszko's health before the killing, she said the cleric suffered from anemia and chronic inflammation of the bladder. Asked if he could have survived bound and gagged in an underground bunker, where the defendants say they initially intended to put Popieluszko to frighten him, Byrdy replied: "That would have been a death sentence."

The autopsy report came at the end of a trial week dominated by close questioning of police Gen. Zenon Platek, the suspended head of the Interior Ministry department in which the accused officers served.

The general was pressed by lawyers representing Popieluszko's family about his seeming slowness to connect to the crime a ministry car seen the night of the killing in Bydgoszcz, near the scene of the priest's abduction.

Questions were also raised in court about why it took the general nearly two weeks to come to suspect his deputy, Col. Adam Pietruszka, on trial with the three junior officers for aiding and abetting them.