In a sharply worded protest, Poland's Roman Catholic church has warned the government of damage to church-state relations caused by attacks on the clergy during the trial of four secret police agents accused of killing a pro-Solidarity priest. The church also complained that trial coverage by the state-controlled press had been biased.

The objections were conveyed in a letter to communist authorities made available to western reporters today on the eve of a scheduled verdict in the trial of the accused slayers of the Rev. Jerzy Popieluszko.

The letter, signed by Archbishop Bronislaw Dabrowski, secretary of the Polish episcopate, accused the official media of "tendentiously" reporting the case by playing up attacks against the church from defendants, some witnesses and government prosecutors, while censoring key sections of rebuttals from attorneys close to the church leadership who are representing the slain priest's family in the Torun court.

"Taking into consideration the fact that the mass media in Poland is a state monopoly, one has to draw the conclusion that someone finds it especially important to disturb church-state relations," Dabrowski said. "In the name of the episcopate, I submit an official protest against such methods of manipulating information and public opinion."

Communist papers have given extensive coverage to the trial, which opened Dec. 27, and Polish radio has carried half-hour broadcasts nightly of recorded testimony. But allegations at the hearing against Popieluszko and the church, Dabrowski said, had rendered the "shameful act of murdering Father Jerzy Popieluszko somehow a secondary problem," pushing it "into the background of this trial."

The letter, dated last Friday, was addressed to Religious Affairs Minister Adam Lopatka with copies going to the director of the Polish press agency and the chairman of the state radio and television committee. It said the church had been inundated with messages expressing embarrassment and indignation at the publicity given allegations of illegal and improper conduct by Popieluszko and other clergymen.

The allegations were allowed in testimony on the ground that they helped explain the defendants' motives for the crime. The cashiered police captain who led the kidnapers, Grzegorz Piotrowski, said that he was driven to take illegal action out of frustration at the tolerance shown the church by the government.

A lengthy impassioned attack by Piotrowski listing alleged improprieties by clerics and tax privileges granted the church was given wide publicity. So was a summation by the public prosecutor, who revived never-proven allegations about Popieluszko as a major political underground activist. The prosecutor blamed what he called the priest's political extremism for his death.

Concurrent with the trial, there has been a significant increase in Polish press accounts of unflattering or embarrassing incidents for the church. The editor of Warsaw's main daily paper observed last week that the trial has broken two taboos -- one on publicizing crimes committed by the secret police, the other on reporting controversial church activities.

This rise in critical church coverage has been explained by some Poles as an attempt by the communist leadership to balance the discomfort suffered by the security apparatus at seeing several of its own agents stand public trial.

Adding to the impression of a stiffer government line toward the church, Religious Affairs Minister Lopatka complained last week that church officials were still "too tolerant" toward the "militant clericalism of certain priests."

Government spokesman Jerzy Urban joined the offensive, saying that the authorities are considering adopting regulations to protect the rights of nonbelievers, similar to existing protections for the faithful.

At a regular weekly press conference yesterday, Urban defended official reporting of the trial and termed the attacks on Popieluszko justified. "Whoever engages in public activity, whoever gets involved in politics publicly, must in a way accept . . . that his activity may be material for discussions and critical analyses," Urban said.

The letter marked the second complaint about media coverage of church affairs from the church hierarchy in a month. Cardinal Jozef Glemp objected in a Jan. 6 sermon to a television report that he said sought to portray the church as "malicious."