Poland's Catholic Church is preparing for more upheaval with the upcoming release of a book that will name 39 priests who acted as secret police informants during the country's Communist era.

Rev. Tadeusz Isakowicz-Zaleski, a priest in Krakow, told the New York Times on Tuesday that he will publish a book in mid-February that will feature a list of priests who collaborated with the secret police. Three of the 39 are now bishops in Poland.

The revelations are expected to increase controversy surrounding the church, already in upheaval because Warsaw's new archbishop, Stanislaw Wielgus, resigned on Sunday after admitting he co-operated with the secret police in the Communist era.

Another senior clergyman, Rev. Janusz Bielanski, the rector of Krakow's Wawel Cathedral, resigned on Monday because of the upcoming allegations, but said on Tuesday he was never an informer.

Polish Prime Minister Jaroslaw Kaczynski said Tuesday the controversy has become a "national crisis."

Kaczynski said the scandal threatens to do major damage to the church, which he described as a religious institution in Poland.

The Catholic church plays a powerful role in the country, ruled by the Communists until 1989.

Zaleski told the Times that he found the names of the 39 priests in the files of secret police in Krakow. He said he tried to contact all of them for comment, but only 22 responded, with four admitting they were collaborators. The majority denied they had any links to the secret police.

Bielanski was among those who replied.

Zaleski said he had been told by the Krakow archbishop, Cardinal Stanislaw Dziwisz, in a June meeting that he needed to obtain comment from the priests he planned to identify before he published his findings. Initially, Dziwisz said he was forbidden from naming the priests.

According to the Times report, the Catholic church continued to be a force in Poland in its Communist years, more so than in other Communist countries, because Archbishop Stefan Wyszynski, the most senior figure in the Polish Catholic church at the time, agreed to work with the authorities.

Historical estimates

Historians from the Institute of National Remembrance, run by the Polish government, estimate that about 15 per cent of Polish priests co-operated with the Communist-era intelligence services.

Kaczynski said Tuesday the church played a positive role in trying to oppose the Communist regime, but he said the current crisis is casting a pall over the church, suggesting it played an active role in maintaining the Communist regime.

Wielgus resigned less than an hour before his scheduled installation, announcing his decision at Warsaw's St. John's Cathedral.

The church was packed with worshippers gathered for a mass that was to have marked his formal installation. The congregation included President Lech Kaczynski.

Pope Benedict XVI, who appointed Wielgus just a month ago, accepted his resignation.

With files from the Associated Press