Pope Benedict XVI on Saturday authorized wider use of the long-marginalized Latin Mass, a move that delighted Roman Catholic traditionalists but worried others who fear the erosion of important church reforms.
Revival of the old service, which had been largely supplanted by the modernizing spirit of the Second Vatican Council, also angered Jewish groups because it contains a passage calling for the conversion of Jews.
In a decree known as a motu propio, essentially a personal decision, the pope urged priests to celebrate a 1962 version of the 16th century Tridentine Mass when their congregations request it.
Until now, priests could use the Latin Mass only with permission from their bishops, which was not always forthcoming.
The much-anticipated decision, nearly two years in the making, is an attempt to win back disaffected conservatives and to unite the church, Vatican officials said. It is also a reflection of Benedict's personal preference for traditional liturgy and incantations in Latin, a language he extols as beautiful and holy.
"What earlier generations held as sacred remains sacred and great for us too, and it cannot be all of a sudden entirely forbidden or even considered harmful," the pope wrote in the decree.
But his announcement risks alienating some faithful. It could sow rather than mend divisions, undermine other reforms and harm interfaith relations, several church leaders and Catholic experts said.
The Tridentine Mass was largely replaced by newer liturgy approved during the Second Vatican Council, which took place from 1962 to 1965. In the newer rite, local languages replaced Latin, priests faced their congregations instead of turning their backs on them, and some wording deemed offensive to Jews was changed.
Attempting to reassure the doubters, Benedict said Saturday that since both the Tridentine Mass and the more modern liturgy would be available, there should be no concern that the church was turning back the clock.
"This fear is unfounded," he said in a letter to the world's bishops that accompanied his decree.
Benedict noted that the older liturgy was never outlawed; rather, he wrote, it fell out of favor in part because some bishops thought its use would challenge the broader Vatican II reforms.
But the reforms were sometimes misinterpreted as "authorizing or even requiring creativity," he wrote, deforming the liturgy and driving people from the church.
"I am speaking from experience, since I too lived through that period with all its hopes and its confusion," wrote the former Cardinal Joseph Ratzinger, longtime watchdog of church dogma. "And I have seen how arbitrary deformations of the liturgy caused deep pain to individuals totally rooted in the faith of the church."
The Tridentine Mass, named for the 1545 Council of Trent, which spent two decades codifying the Latin rite from earlier liturgies, will not become common, the pope said, because so few people can speak or work in Latin. The Vatican II version remains the predominant form.
Benedict dismissed arguments that the existence of two versions might splinter the church.
"It is not appropriate to speak of these two versions of the Roman Missal as if they were 'two rites.' Rather, it is a matter of a twofold use of one and the same rite," he wrote.
The pope has long held that suppressing the old liturgy essentially set one version against the other, said Father Thomas Rausch, a theologian at Loyola Marymount University who is writing a book about Benedict's theological outlook.
"He sees that as a wound and he wants to heal it," Rausch said.
Some of the strongest criticism Saturday came from proponents of interfaith dialogue and from Jewish organizations. Although references to "perfidious Jews" have been removed from the old liturgy, its Good Friday prayers contain a call for the conversion of the Jews and for God to lift the "veil from their hearts" so that they might know Jesus Christ.
"This is a theological setback in the religious life of Catholics and a body blow to Catholic-Jewish relations," Abraham H. Foxman, national director of the Anti-Defamation League, who is in Rome for meetings with Vatican officials, said in a prepared statement. "It is the wrong decision at the wrong time."
Rabbi Abraham Cooper, associate dean of the Los Angeles-based Simon Wiesenthal Center, called on the pope to publicly repudiate such language, which is contrary to the teachings of today's church.
"Obviously, we are disappointed that Pope Benedict didn't take the opportunity to permanently sideline the problematic references in the earlier liturgy," he said.
Many older Catholics grew up with the Latin Mass and, along with a number of younger worshipers, regard the pre-Vatican II rite as more authentic, more reverent and more mystical.