The Vatican said Monday that Pope Francis had allowed priests to bless same-sex couples, his most definitive step yet to make the Roman Catholic Church more welcoming to L.G.B.T.Q. Catholics and more reflective of his vision of a more pastoral, and less rigid, church.

The Vatican had long said it could not bless same-sex couples because it would undermine church doctrine that marriage is only between a man and a woman.

But the new rule made clear that a blessing of a same-sex couple was not the same as a marriage sacrament, a formal ceremonial rite. It also stressed that it was not blessing the relationship, and that, to avoid confusion, blessings should not be imparted during or connected to the ceremony of a civil or same-sex union, or when there are “any clothing, gestures or words that are proper to a wedding.”

Blessings instead are better imparted, the Vatican says, during a meeting with a priest, a visit to a shrine, during a pilgrimage or as a prayer recited in a group.

The new rule was issued in a declaration, a rare and important Vatican document, by the church’s office on doctrine and introduced by its head, Cardinal Víctor Manuel Fernández, who said that the declaration did not amend “the traditional doctrine of the church about marriage,” because it allowed no liturgical rite that could be confused with the sacrament of marriage.