VATICAN CITY (AP) – Bishops from around the world begin tackling major issues facing the Roman Catholic Church today, including whether Holy Communion should be given to Catholic politicians who back abortion rights and to divorced people who remarry without getting an annulment.

The priest shortage, and whether celibacy contributes to it, as well as dwindling Mass attendance also are expected to be discussed at the three-week Synod of Bishops, during which bishops will offer recommendations to Pope Benedict XVI on running the church.

The Vatican said Saturday that 256 bishops from 118 countries would participate – the most ever. In addition, 10 representatives from non-Catholic Christian churches will attend, although they do not have voting rights.

Benedict formally opens the synod with a Sunday Mass, and in many ways the meeting is as much about him as it is about the bishops since it is the pontiff’s first major Vatican undertaking since being elected April 19.

Many participants have pointed to the changes Benedict made in organizing the synod as evidence he wants it to be a more collegial exchange of ideas than a meeting with a preordained outcome. Bishops will speak for six minutes rather than eight, allowing for an hour of open discussion at the end of each day.

“That in itself, while subtle, is a real emphasis,” said Pittsburgh Bishop Donald Wuerl, one of the American delegates attending the Oct. 2-23 meeting.

Officially, the synod will discuss the Eucharist, or the sacrament of Holy Communion, which Catholics believe is the body and blood of Christ. But a range of issues falls under that.

In the draft document outlining the synod agenda, the Vatican singled out divorcees who remarry without getting an annulment and Catholic politicians who support abortion rights in criticizing those who continue to receive Holy Communion while in a state of “mortal sin.”

The Rev. Anthony Figueiredo, a special assistant to the pope during the synod, said he expected debate on both topics but little change in church policy.

“I think what we will be seeing is a very clear affirmation of fidelity to the church’s teaching,” he said.

The document also noted declining Mass attendance – in some countries, only 5 percent of the faithful attend – as well as the priest shortage. It cited statistics showing there was one priest for every 1,797 Catholics in 1978 compared with one priest for every 2,677 Catholics in 2003.

Because of the shortage, several participants said they expected the church’s celibacy requirement to be discussed since many believe that more men would join the priesthood if they were allowed to marry.

“They’re certainly not going to talk about ordination of women, but I think there might be some discussion of the celibacy law,” said the Rev. D. Francis Moloney, an Australian theologian at the synod.

A survey by two U.S. church reform groups of more than 15,000 priests in 55 American dioceses said 67 percent believed that mandatory celibacy should be discussed. Sister Christine Schenk of the FutureChurch group said she planned to deliver the survey results and petitions from parishioners to church officials during the synod.

“It has been very unbelievable to me that steps have not been taken prior to this time to address the problem that has led to parishes closing and clustering,” she said.

Benedict invited four Chinese bishops to attend the synod as part of his effort to unify China’s divided church. But as of Saturday, the bishops had not submitted the necessary paperwork to attend, Vatican officials said – an indication the Beijing government would not let them come.

Nevertheless, Monsignor Nikola Eterovic, the general secretary of the synod, remained hopeful.

“We remain open to receiving them, even until the last day,” he said.

During previous recent synods, one topic of “sideline” discussions has always been the papal succession. With Benedict now in office, that perennial issue may be replaced by an upcoming Vatican document expected to reaffirm the church’s belief that homosexual men should not be ordained.

“The bishops might talk about it personally, but it’s not a focal point in the discussion about the Eucharist,” said Bishop William Skylstad, president of the U.S. Conference of Catholic Bishops.