Victoria police made the assessment in a submission to a state parliamentary inquiry into child abuse, the Australian Broadcasting Corp. reported Wednesday.
The document says the church appears to have dissuaded victims from reporting abuse, alerted suspects to allegations and moved or protected suspected offenders.
Police also were critical of the church's complaint system and said the church's chief investigator had persuaded victims not to go to the police.
In a separate submission, Victoria church leaders urged lawmakers to preserve the sanctity of the confessional in considering any changes in existing law.
"Legislation requiring priests to violate the sacramental seal of confession will be ineffective as priests will be unable and unwilling to comply," the submission said.
Over the past 16 years, the church has upheld 620 complaints, most of which was committed in the 1960s, '70s and '80s, the document added.