A New South Wales Catholic priest has pleaded guilty to molesting dozens of boys on separate occasions in the 1970s and 80s.

John Sidney Denham was originally charged with 134 child sex offences relating to 39 boys in Sydney, Newcastle, the Hunter Valley and the state's mid-north coast.

Today he pleaded guilty to 29 offences, with the bulk of the other charges withdrawn.

Most of the victims were molested while they were students at St Pius X High School at Adamstown in Newcastle.

Denham was charged by Strikeforce Georgiana, which has laid more than 170 charges against three priests and another member of of the clergy over the past year.

The other priests are still awaiting trial. Denham will be sentenced later this month.