A Polish court found three secret police agents guilty today of the kidnaping and murder of a pro-Solidarity Roman Catholic priest and convicted a fourth of instigating the crime, pronouncing long prison sentences on all.

The acknowledged leader of the murder team, former captain Grzegorz Piotrowski, was sentenced to 25 years, although the prosecutor had sought the death sentence.

In a surprising move, the court also ordered a 25-year prison term -- the maximum penalty short of the death sentence -- for Adam Pietruszka, the demoted police colonel who had insisted he was innocent of charges of aiding and abetting the killers.

Two former police lieutenants who participated in the murder of the Rev. Jerzy Popieluszko received lesser jail sentences: 15 years for Leszek Pekala and 14 for Waldemar Chmielewski.

As the verdicts were read in a crowded courtroom in the north-central Polish town of Torun, Piotrowski, 33, cool and confident throughout much of the six-week trial, wiped his face with a handkerchief and put his head in his hands. Pekala, 32, sobbed, and Chmielewski, 29, suffering from a nervous disorder reportedly induced by his arrest, trembled in the wooden dock.

Only the stony-faced Pietruszka, 46, a veteran of the Interior Ministry, showed no outward reaction, according to courtroom observers.

Although the judgment appeared merciful in the case of Piotrowski, who many had expected would be sentenced to die, it was noted that lawyers for Popieluszko's family had asked that his life be spared, saying the slain priest had opposed capital punishment and would have offered forgiveness had he lived.

Delivering the decision, Chief Judge Artur Kujawa said he had received more than 1,000 letters, a number of which supported the prosecution's demand that Piotrowski be hanged, but he explained that Polish law should not be used for revenge.

Disputing claims by the defendants that they had never intended to kill Popieluszko, only to kidnap and frighten him, the judge said the four were convicted because they had "the objective of killing Popieluszko, and they accomplished it." He said they were fully aware that they were acting illegally and he stressed that regulations of the Interior Ministry do not allow illegal methods.

Most remarkable was the harsh sentence for Pietruszka, who had supervised the three junior officers as deputy director of an Interior Ministry department responsible for monitoring church activities. Evidence against him consisted largely of charges by the other defendants that he had encouraged illegal action to curb the outspoken priest's activities and had provided them with travel documents and a special road pass that facilitated the abduction.

Several ministry employes also gave damaging testimony implicating him in a cover-up attempt, saying he had censored harmful references to himself in investigative reports and concealed the license number of the car used in the abduction.

The judge termed Pietruszka's involvement "a necessary condition for the success of the whole operation," ensuring freedom of action for his subordinates in carrying out the murder. "His crime was a crime committed behind the desk, but it was a particularly cynical one," Kujawa said.

Lesser sentences for the two former lieutenants reflected their position not just as perpetrators but also as victims of the designs of their superiors, the judge said.

For Poland's ruler, Gen. Wojciech Jaruzelski, the sensational trial has been an attempt to mollify public outrage over the killing and gain western sympathy by appearing to meet demands for full disclosure and justice. But Poland's powerful Roman Catholic Church has complained that the trial was used as a forum for accusations of political extremism by Popieluszko and allegations against other clerics. This week, the church accused the communist press of biased coverage of the trial and warned of damage to church-state relations.

Absent from the courtroom today were representatives of the church, members of Popieluszko's family and the dead priest's friend and driver, Waldemar Chrostowski, all of whom had attended the court sessions regularly.

The Roman Catholic Church said it would issue a statement after a Feb. 13-14 meeting of the country's bishops, but a spokesman in Warsaw said prison terms were severe enough punishment, The Associated Press reported.

Earlier, in remarks similar to those expressed by many Poles, Stanislaw Popieluszko, a brother of the priest, said: "I don't know whether we'll ever know the whole truth. But my feeling is that more names should have been involved."

The proceedings opened a rare window onto the abuse of power, ineptitude and arrogance of the shadowy security apparatus. Access to the trial, including attendance by a restricted number of western correspondents, was highly unusual in the Soviet Bloc, where secret police seldom are held accountable for breaking laws.

To limit an erosion of morale in the police establishment, communist officials have described the defendants as aberrations, and praised the efforts of the Interior Ministry in tracking them down.

The killing was recounted in exhaustive detail in the trial, beginning with Popieluszko's kidnaping Oct. 19 on a road north of Torun by the defendants, disguised as militiamen. They put the priest in the trunk of their Fiat, but the driver, Chrostowski, escaped by jumping from the car and set off a national outcry over the priest's fate.

Popieluszko tried to flee but was clubbed senseless on four occasions and finally was tossed off a dam -- bound, gagged and possibly still alive -- into a Vistula River reservoir at Wloclawek, northwest of Warsaw.

The defendants retracted pretrial statements that had implicated higher-ups in the ministry, saying they had come to realize no one beyond Pietruszka was aware of the plot. The prosecutor concluded last week that the trial showed no one else in the ministry was involved.

But attorneys for both the state and Popieluszko's family suggested in closing statements that instigation for the crime may have come from abroad. The prosecutor pointed to western "centers of subversion," and a Popieluszko family lawyer with close ties to the church leadership suggested that the Soviet secret police might have played a role.

Other suspicions focused on the role of a police general, Zenon Platek, the suspended head of the department in which the defendants served. From his and other testimony, Platek appeared to have been slow to act on an early report that a ministry car was seen the night of the kidnaping in Bydgoszcz, where Popieluszko preached before he was abducted. Platek also claimed not to have suspected his deputy, Pietruszka, of involvement until shortly before Pietruszka was arrested, two weeks after the crime. Platek has not been charged.