Pope John Paul II said in a surprise announcement Tuesday that he would issue a new encyclical on the social problems of the 20th century.

The announcement came in the homily of a Mass at St. Peter's Basilica celebrating the Roman Catholic Church's World Day of Peace.An encyclical, the highest form of papal writing, is a pastoral letter to the entire church. It will be the pontiff's eighth encyclical since his election in 1978.

He also proclaimed 1991 the "Year of the Social Teaching of the Church" and urged Catholics to become more familiar with Roman Catholic social doctrine, which includes teachings on issues such as justice, peace and work.