WARSAW, Poland (AP) _ A Roman Catholic priest convicted on charges of aiding those who murdered a Warsaw policeman has been on a hunger strike for two weeks demanding political prisoner status, a Solidarity activist said Wednesday.

The priest, the Rev. Sylwester Zych, began his hunger strike May 15 at Braniewo Prison in northeastern Poland after being kept alone in a cell for nine months, according to Zbigniew Romaszewski, a prominent Warsaw Solidarity activist.

Zych was joined in his fast at Braniewo by an imprisoned Solidarity activist, Jozef Sreniowski, who is serving a two-year sentence for distributing underground publications, Romaszewski said in a telephone interview.

''It is a strict fast without any deadline which is intended to end the isolation of Father Zych,'' said Romaszewski. ''They drink only water, but are not force-fed now.

''Father Zych has remained alone in his cell for nine months as he has been refused the rights of a political prisoner,'' Romaszewski said.

He added that the priest refused to share his cell with common criminals and was not allowed to contact political prisoners at Braniewo.

Zych, 35, is serving a six-year sentence after being convicted of hiding a pistol used to kill a police officer, Sgt. Zbigniew Karos, during a scuffle on a Warsaw streetcar in February, 1982.

Zych and seven youths accused of being members of a group responsible for the Karos shooting were convicted by a Warsaw military court in 1982.

Meanwhile, Minister for Religious Affairs Adam Lopatka said Wednesday that Poland's Communist government respects religious freedom, but opposes church interference in secular affairs.

''Those churches ... going beyond their religious mission are engaged in nothing more than clericalism, that is, trespassing upon those domains of life which are of a secular character,'' said Lopatka in an article published in the official Communist Party daily Trybuna Ludu.

''Clericalism flagrantly violates the principle of separation of churches ... from the state. Any kind of clericalism is a harmful phenomenon.''

The article appeared after the government indicted two priests on charges of leading a sit-in strike by several hundred students and parents last December to protest removal of crucifixes from a state-run vocational high school in the southern town of Wloszczowa.

The Revs. Marek Labuda and Andrzej Wilczynski are to go on trial Monday on charges of organizing an illegal protest and breaking into the school building, a spokesman for the southern Kielce diocese said.

The Wloszczowa school sit-in was one of the most serious confrontations in the ''war of the crosses'' during which Roman Catholics protested orders by Communist authorities to remove crucifixes from public buildings.