VATICAN CITY — In a marked shift in tone likely to be discussed in parishes around the world, an assembly of Roman Catholic bishops convened by Pope Francis at the Vatican released a preliminary document on Monday calling for the church to welcome and accept gay people, unmarried couples and those who have divorced, as well as the children of these less traditional families.

The bishops’ report, issued midway through a landmark two-week meeting, does not change church doctrine or teaching, and will now be subjected to fierce debate and revision at the assembly.

But it is the first signal that the institutional church may follow the direction Francis has set in the first 18 months of his papacy, away from condemnation of unconventional family situations and toward understanding, openness and mercy.

Previous synods have produced little, but some participants in this one have likened it to the historic Second Vatican Council convened just over 50 years ago, which produced monumental changes in church liturgy, relations with other faiths and the conception of the roles of priests and laypeople.