Concerned by the declining number of Sunday churchgoers, Pope John Paul II issued a sweeping call for Roman Catholics to respect the Lord's day.

In a 100-page apostolic letter released Tuesday, he urged believers not to confuse "the celebration of Sunday" with a " `weekend,' understood as a time of simple rest and relaxation."Those who don't go to Mass regularly "should be convinced that they cannot live their faith or share fully in the life of the Christian community," he said.

The custom of the "weekend" and a declining sense of faith have kept people out of church, the pope said.

Vatican officials at a news conference to introduce the "The Day of the Lord" letter gave examples: In Austria, only 17 percent attend Mass; in Rome itself, 28 percent.

The document offers John Paul's vision of the meaning of Sundays. It was formulated by his years as archbishop in Krakow, Poland, and regular Sunday visits to Rome parishes as pope.