ROME — In an extraordinary gesture of clemency, Pope Francis announced Tuesday that during a special Holy Year of Mercy set to begin Dec. 8, every priest in the world will be able to forgive the sin of abortion, and anyone who confesses their sins to a priest of a breakaway traditionalist group will be considered validly forgiven.

Given that both abortion and defiance of papal authority are considered extremely serious sins under Church law, the moves will be seen as a major effort to reach out to alienated groups.

Although the pope’s language on abortion in a letter released by the Vatican Tuesday refers primarily to women who have had one, the gesture also could be interpreted to apply to other parties involved, such as the medical personnel who carry out the procedure.

In the letter, Francis says he knows well the “moral and existential ordeal” experienced by many women who have been through an abortion.

“I think in particular of all the women who have resorted to abortion. I am well aware of the pressure that has led them to this decision. I know that it is an existential and moral ordeal. I have met so many women who bear in their heart the scar of this agonizing and painful decision. What has happened is profoundly unjust; yet only understanding the truth of it can enable one not to lose hope. The forgiveness of God cannot be denied to one who has repented…”

Regarding the traditionalist Society of St. Pius X, Francis says that bishops from around the world have told him about the “good faith and sacramental practice of the faithful who attend their churches.”

Stating that the “Year of Mercy excludes no one,” and “motivated by the need to respond to the good of these faithful,” Francis says that anyone who confesses to a priest of the society “shall validly and licitly receive the absolution of their sins.”

One of the bishops praising the traditionalist group may well have been the pope’s fellow Argentine Cardinal Mario Poli, his hand-picked successor in Buenos Aires, who in April welcomed it into the archdiocese.

Speaking on background, Vatican officials took pains on Tuesday to stress that neither concession represents a change to Catholic teaching, in that both abortion and breaking with the pope are still regarded as sinful.

The concession for the Society of St. Pius X, often called the “Lefebvrists” after the deeply conservative late French Archbishop Marcel Lefebvre who founded it in 1970, may strike many observers as especially surprising, given that Francis has generally been seen with suspicion in traditionalist circles.

In his letter, Francis nevertheless expressed hope that the rupture with the society may be overcome “in the near future.”

The pontiff’s letter announcing the moves was formally addressed to Italian Archbishop Salvatore “Rino” Fisichella, who as President of the Vatican’s council for the Promotion of New Evangelization is the man in charge of organizing the extraordinary Year of Mercy, announced by Pope Francis last March.

It’s considered an “extraordinary” jubilee since such event normally occur every 25 years, but Francis decided to move this one up.

When presenting activities for the jubilee year during a Vatican news conference in May, Fisichella said that even though mercy is an aspect of every holy year, the fact that it’s the formal theme this time around is a sign that Francis wants to put confession at the center of the life of the Church.

The Catholic Church considers both abortion and “schism,” meaning the rejection of church authority, as sins that trigger excommunication latae sententiae, meaning automatically. To be able to forgive those sins, a priest needs special permission from a bishop.

Bishops can delegate that authority to their priests in advance, and in many American dioceses prelates over the years have done so with regard to abortion.

When it comes to the Society of St. Pius X, the group has been in open rupture with Rome since 1989, after Lefebvre ordained four new bishops without papal approval. Since 2000 there have been repeated efforts at reunification, but so far to no avail.

In the case of abortion, Francis’ concession is not unprecedented.

During the 2011 edition of “World Youth Day,” a Vatican-sponsored youth festival that takes place in a different city every two or three years, priests were granted the power by Pope Benedict XVI to forgive the sin of abortion without needing their bishop’s approval.

In the letter, Francis calls for priests to fulfill this task by expressing words of genuine welcome combined with a reflection that explains the gravity of the sin committed.

“A widespread and insensitive mentality has led to the loss of the proper personal and social sensitivity to welcome new life,” Francis wrote. “The tragedy of abortion is experienced by some with a superficial awareness, as if not realizing the extreme harm that such an act entails.”

There are no recent cases in which a pontiff has declared that a sacrament delivered by a priest considered to be in schism will nevertheless be recognized as licit.

In 1995, the Vatican issued a document saying that while priests of the Society of St. Pius X have been validly ordained, they are considered suspended a divinis, meaning legally prohibited from exercising ministries such as the sacrament of confession, because they were ordained without papal authorization.

In the letter, Francis also says that during the Holy Year, those who for extraordinary reasons, such as illness or imprisonment, can’t personally participate in the activities to be carried out around the world, will also be able to benefit from them.

“Living with faith and joyful hope this moment of trial, receiving communion or attending Holy Mass and community prayer, even through the various means of communication, will be for them the means of obtaining the Jubilee Indulgence,” Francis said, referring to a special form of forgiveness of sins available during the year.