A Polish secret policeman broke down and sobbed repeatedly in court today as he described the last hours of Warsaw priest Jerzy Popieluszko, his fears of discovery after the killing, his decision to confess and his belief that his involvement had cost him his young family.

Observers in the restricted courtroom in Torun where four Interior Ministry officials are on trial for the killing described the day's emotional testimony as the most dramatic so far in the week-old hearing.

His eyes tearing and right cheek twitching violently from a nervous disorder apparently suffered since the killing, 29-year-old Waldemar Chmielewski told the court he had begun to panic about being discovered immediately after the Oct. 19 slaying. He grew suspicious, he said, fearing that he was being followed and worrying he would take all of the blame for the crime.

Chmielewski, a lieutenant at the time of the killing, is accused along with ex-lieutenant Leszek Pekala and ex-captain Grzegorz Piotrowski of abducting Popieluszko on a road north of Torun, killing him and dropping his body in a reservoir on the Vistula River in nearby Wloclawek. The three officers' superior, Col. Adam Pietruszka, is charged with instigating and assisting in the death of the cleric, who was a staunch champion of the outlawed Solidarity trade union.

Chmielewski and Pekala, the only defendants to have given evidence in court so far, have said they took part in the operation because they thought it had high-level authorization. Chmielewski, whose nervous condition has deteriorated visibly during his three days on the stand, was allowed to remain seated while testifying today and was granted periodic rests in accordance with doctors' recommendations to the court yesterday.

Chmielewski said he had expressed his fears to his boss, Piotrowski, who repeatedly assured him not to worry and advised him to remain calm. But the captain did instruct him to change the license plates on the car used to abduct the priest because the numbers had been noted by militiamen in Bydgoszcz shortly before Popieluszko was seized.

Chmielewski said Piotrowski also ordered that no discussion about the assassination take place at the Interior Ministry. He said the captain had been warned by Pietruszka that ministry offices had been bugged in connection with an investigation into the priest's death.

A special investigation team was set up in the ministry soon after the slaying. Announcement of Popieluszko's disappearance and, 11 days later, the discovery of his body shocked the nation and was quickly interpreted by the government's leader, Gen. Wojciech Jaruzelski, and his close aides as a political provocation aimed at undermining the general's rule.

Three days after the killing, Chmielewski said, he approached Piotrowski to ask what the officers should do to protect themselves from arrest and prosecution. "I was told there was nothing to worry about," Chmielewski recalled. "Piotrowski said the people involved in the investigation are good guys."

Asked by the court to name the people on the investigating team to whom Piotrowski was referring, Chmielewski cited Gen. Zenon Platek, who heads the department in which the four defendants worked, and Zbigniew Jablonski, whose current rank and position are unknown but who previously had held Piotrowski's position as a section chief.

Polish authorities announced Nov. 2 that Gen. Platek, whose department is responsible for monitoring church activities, had been suspended from his duties for lack of supervision. Both Platek and Jablonski are listed among the 22 witnesses scheduled to testify at the trial.

In contrast to his own trepidation, Chmielewski suggested that Pekala and particularly Piotrowski were comparatively relaxed after the killing. He said the two men laughed after phoning the secretariat of the Warsaw bishops' curia on Oct. 21, two days after Popieluszko was killed, to demand a ransom of $50,000 for the priest. The call was made in an attempt to cover their tracks and mislead investigators.

Pekala has testified that he traveled to Poznan in western Poland on Oct. 22 to mail an anonymous letter to the Warsaw curia affirming the ransom request.

Chmielewski's fears, meanwhile, increased when the staff of his department was summoned by Gen. Platek and told to account for their movements on Oct. 19. The meeting was in Pietruszka's office, but neither the colonel nor Piotrowski was present.

"I panicked because the people whom I could ask what to write were not there," Chmielewski said. "Piotrowski was not there, and I thought he was hiding himself somewhere and that all the blame would fall on Pekala and me. I left the room with Pekala and told him angrily that I was going to write that I was ill that day and that he could write what he liked."

But Chmielewski was detained the following day on suspicion of involvement in the killing. At first, he said, he lied about what happened, telling investigators that the priest had been left alive in a forest. But when he heard on the radio Oct. 25 that Piotrowski had been arrested, Chmielewski said he decided to confess all.

Chmielewski said he had felt "cheated and exploited" and resolved to tell the truth because "no one could live with such knowledge."

"It was a cruel and terrible event," he went on tearfully. "No reasonable man could cover it up. That would be beyond human capability."

Indicating that his father also worked for the Interior Ministry, which controls Poland's uniformed and plainclothes police, Chmielewski said remorsefully, "I believed in my chief more than in my father, even though my father worked for the same institution."

He paused, trying to regain some composure. His wife, who is eight months pregnant with their second child, sat in the back of the crowded courtroom, also weeping.

Wiping his eyes, Chmielewski said, stammering badly as he has throughout his testimony: "For all practical purposes, I have lost my family."

Struggling to regain his composure, he continued: "I had my life. I became aware that the priest also had a family -- the people who are suffering. That could not be hidden."

A judge asked him to describe Piotrowski. Chmielewski spoke of the captain in admiring terms, calling him an excellent supervisor, skilled at explaining things clearly, a man of strong character who had inspired Chmielewski to do well and win awards. The 33-year-old Piotrowski, who had sat unmoved during much of the trial, tucked his head down at this, seeming to hide a show of emotion.

In his three days on the stand, Chmielewski has said he was a reluctant participant in the crime, placing most of the responsibility on an insistent Piotrowski and depicting Pekala as something of a cynic.

Earlier today, he recalled the final moments of Popieluszko's life as the officers drove southeast out of Torun toward the reservoir with the priest, bound and gagged, in the trunk of their Polish-made Fiat. Piotrowski, he said, refused requests by the lieutenant to leave the cleric alive.

But Chmielewski admitted to some direct involvement in the killing. He said he called out to the others when Popieluszko appeared to be struggling out of the trunk. The officers stopped, and the priest was beaten unconscious.

Chmielewski said he also helped tie bags of stones to the priest's feet and, with his two colleagues, tossed the body into the reservoir. He gave the impression that the confusion and fear he was feeling at the time had, paradoxically, driven him to take part in the killing.

He said Popieluszko must have died from the severe beatings dealt mostly by Piotrowski at several stops after the abduction.

This conclusion contradicted the findings of an official autopsy, which ruled that the death was the result of suffocation caused by a gag, by pressure from a noose around Popieluszko's neck or by blood from wounds in the priest's nose and mouth choking the frail 37-year-old cleric.

"No person could have survived so many blows to the head," Chmielewski said to a hushed courtroom. "I am convinced the cause of death was beating."

The trial adjourned for the weekend, with Chmielewski due to resume testifying Monday.