A secret police captain who led the abduction and murder of the Rev. Jerzy Popieluszko said today the death was unintentional and sought to transfer ultimate responsibility for it to government authorities and Roman Catholic church officials who failed, he said, to curb the cleric's allegedly illegal activities.

Grzegorz Piotrowski, on trial for the killing, spoke of his frustration at seeing Popieluszko go unrestrained. He said he decided to take what he knew was illegal action against the outspoken priest because "a lesser evil is sometimes necessary to prevent a greater evil."

Some Poles who heard him say this phrase shuddered, associating it with the justification given by Polish leader Gen. Wojciech Jaruzelski when he declared martial law to stop the Solidarity union movement in December 1981.

Appearing calm and self-assured during seven hours of testimony at the Torun provincial court, Piotrowski buttressed earlier statements by two subordinates, Leszek Pekala and Waldemar Chmielewski, also accused of the murder, who said they thought they were carrying out a mission that had been approved by high officials.

But Piotrowski admitted he had no proof that such authorization had existed and said he now realizes "the only higher-up" behind the crime was his supervisor, Col. Adam Pietruszka, on trial with the three junior officers on charges of aiding and abetting them.

Speaking from notes in a relaxed voice that contrasted sharply with the nervousness shown on the stand by the two policemen who testified before him, Piotrowski discussed his motivation for moving against Popieluszko. He refuted the indictment's allegation that he had acted out of hatred. He described his attitude toward the priest as "one of indifference and official coolness," but professed to have been annoyed at the government's failure to take legal measures against what he said were Popieluszko's extensive underground activities.

As head of a section in the Interior Ministry monitoring church activities, Piotrowski, an award-winning officer with a college degree in mathematics, said he closely watched Popieluszko's contacts with the West, his involvement in underground educational structures and what he said were Popieluszko's efforts to link underground networks of major cities.

Piotrowski said his frustrations grew when a charge against the priest for abusing religious rights was dropped under a broad amnesty last summer.

"Popieluszko continued his activities and we could only watch," Piotrowski said. "It was then that I agreed to take illegal action. I concluded that a lesser evil is sometimes necessary to prevent a greater evil," an apparent reference to Popieluszko's alleged efforts to build up the underground.

"I am convinced that neither I nor Chmielewski nor Pekala would have found ourselves in the dock if the law had been the law also for Fr. Popieluszko," he stated.

Pietruszka, Piotrowski's superior, apparently was similarly upset, not only about Popieluszko but also about another defiant Warsaw cleric, the Rev. Stanislaw Malkowski.

In early September, Piotrowski said he was summoned to a meeting with Pietruszka along with Leszek Wolski, a lieutenant colonel in the Warsaw internal affairs office also monitoring Popieluszko, and told firmly and excitedly by his boss: "Enough of games with Popieluszko and Malkowski. They should be shaken to bring them to the verge of a heart attack. They should be given a final warning."

At Piotrowski's suggestion, Popieluszko was selected as the first target, because he was "politically more dangerous." Wolski was given the assignment to prepare a plan. Before leaving, Pietruszka said: "I don't have to tell you comrades that this is the decision of a high level," or highest level, Piotrowski recalled, unsure of which formulation Pietruszka had used.

At another meeting in late September, attended by Gen. Zenon Platek, Piotrowski quoted Pietruszka as admonishing Wolski for dragging his feet on the project. But Piotrowski told the court, "I don't know if Platek was aware of what Pietruszka was talking about." The general, head of the department in which the indicted officers worked, was suspended from duty for lack of supervision on Nov. 2.

It was Piotrowski who finally took the initiative. He was sure at the time, he said, that the operation had high-level backing since he knew lesser actions had required the approval of a deputy minister. He and his subordinates speculated that the head of the secret police, Gen. Waldyslaw Ciaston, who is a deputy minister in the Interior Ministry, must have known.

But he told the court today that he now sees "I had no firm proof that any higher-ups existed."