Of the long list of problems the next pope will inherit once the white smoke rises in Rome, few on the diplomatic front can rival the bitter, in­trac­table relationship between the Vatican and the Chinese government.

The two powers have long battled for control over Catholics in China, but the situation has worsened in the past two years to the lowest point in decades. Bishops touted by the government have been excommunicated by the pope. Meanwhile, China’s government has called the Vatican “unreasonable and rude” and stepped up its surveillance and detention of Catholics who remain loyal to the pope in illegal underground churches.

But even as Catholics here responded to Pope Benedict XVI’s retirement with surprise, many took note that his successor is expected to be named within days of China’s own grand conclave next month, when a new generation of top leaders takes control of government.

“It’s an opportunity for the two sides to restart,” said Ren Yanli, an expert on Catholicism at the Chinese Academy of Social Sciences in Beijing.

“Both sides are new,” he said. “They can move forward without historical burdens on their shoulders.”

Even those most optimistic, however, acknowledge that any rapprochement would take much time and require a breakthrough on the conflict at the heart of the rift: which side has final say over who gets ordained in China.

The Vatican maintains that the pope has sole authority in appointing bishops. China’s atheistic Communist Party — long distrustful of what it considers foreign religions — insists that only China should select its church leaders.

The fight between two of the world’s most hierarchical and authority-driven powers has become so fraught that Chinese authorities have in some cases resorted to kidnapping bishops approved by Rome, according to the Vatican, and pressured them into laying their hands upon government-chosen bishops at their ordinations — a move meant to lend such ceremonies legitimacy despite Vatican opposition.

To regular parishioners and priests caught in the middle, the choice comes down to obeying their earthly rulers or their spiritual ones.

Trying to explain the toll of that struggle, one conflicted priest at a state-run church in Beijing quoted this verse from the Bible: “No servant can serve two masters. He will either hate one and love the other, or be devoted to one and despise the other.”

Yet that is the daily reality. He, like many Catholics from both camps, spoke on the condition of anonymity, noting that reprisals against those who question the state church have grown more frequent, especially against those worshiping in churches that aren’t registered with the government.

‘Underground churches’

Nearly half of the estimated 12 million Catholics in China are believed to attend such “underground churches” in remote buildings or private homes, according to foreign experts. The rest worship in official, state-backed churches overseen by a government-run body called the Chinese Catholic Patriotic Association.

In doctrine, the association differs little from the Vatican except for the one tenet fundamental for most Roman Catholics — the primacy of the pope. The association was established in 1957 to ensure Chinese Catholics’ loyalty to their country rather than to the Vatican, which party leaders have long seen as a potentially meddlesome foreign influence. As a result, many Catholics, including some who serve and worship in the state church, harbor reservations about the association’s leadership.

“I go to the official churches to feel that link between God and me when standing in the cathedrals,” said a 23-year-old parishioner in Beijing, describing the tall Gothic architecture and votive candles that are missing from the underground churches. “But I never take communion at the official churches.”

Instead, she receives the sacrament at an underground church. “That’s where I have the feeling of safety, where I can get pure physically and spiritually.”

A convert who was baptized three years ago said his recent decision to stop attending official churches came down to the preaching. State priests seemed to pick their topics carefully, avoiding subjects that could offend the government.

Christianity is about speaking God’s truth, he said. “They just glide over difficult issues.”

The rift and the constant questioning of legitimacy on both sides is one reason, many experts believe, that Catholicism has stalled in China, compared with booming growth in Protestant faiths.

The government pegs Chinese Protestants at 23 million, but foreign analysts estimate them at 58 million or more. Recruiting Catholic priests in China also is increasingly difficult. In the past year, at least two seminaries have closed.

A shattered truce

What has made the diplomatic breakdown at the end of Benedict’s tenure all the more disappointing is the momentum he began with in 2005, when both sides seemed to be inching toward compromise.

In a 2007 letter to Chinese Catholics, Benedict suggested renewing negotiations. He also promised that the church was not looking to overthrow China’s leaders and talked of moving the Vatican’s diplomatic offices from Taiwan to Beijing, ending a vestige from 1951, when China expelled foreign priests and cut diplomatic ties with the church in Rome.

Beijing responded to the pope’s opening with enthusiasm, sending the China Philharmonic Orchestra to play at the Vatican.

For China, making peace with the Vatican showed that the country was opening up to the world as it approached the 2008 Olympics and 2010 Shanghai Expo. At stake for the Vatican was fear that the growing rift could create a separate new church, like the Church of England under King Henry VIII.

After quiet negotiations, the two powers struck a tacit agreement allowing them to save face: They would ordain only bishops acceptable to both sides.

But the informal truce was shattered without explanation just a month after the Shanghai Expo ended in 2010, when Chinese officials ordained a bishop in northeastern China without Vatican approval for the first time in four years.

Other ordinations followed. Then came reports from Catholic witnesses in those regions that papal-approved bishops were ­being forced to attend the government-organized ordinations. The Vatican issued a reminder that any bishop participating in unsanctioned ordinations could face serious sanctions.

Stories of bishops going into hiding and police standing guard outside cathedrals were reported by Catholic news agencies in Asia. One bishop was described as sobbing when authorities dragged him away to an ordination opposed by the Vatican.

A controversial ordination

Anthony Liu Bainian, perhaps the most powerful leader in the state-backed church and one who has been singled out for criticism by the Vatican, blamed Rome for the broken truce.

In an interview last week, he praised the pope as a loving man but criticized the pope’s “working staff on China affairs,” saying they had “an unfriendly, even hostile attitude toward China.”

Liu said Chinese officials told the Vatican repeatedly about the 2010 candidate, Guo Jincai, before his ordination. But, Liu said, the Vatican refused to approve Guo because of his ties to the Communist Party.

“They just don’t want bishops to support socialism. They hope China becomes like Eastern Europe,” he said, an apparent reference to the late Pope John Paul II’s key role in ending communism in Poland.

The Vatican said that it made its opposition clear in advance and called Guo’s ordination humiliating, offensive and “a painful wound upon ecclesial communion.” The Vatican did not explain its objections, but Guo occupied a top position in the Chinese Catholic Patriotic Association and was described by the Vatican’s Asia news agency as “pampered by the regime.”

Many Chinese and foreign experts attribute China’s break from the Holy See to a wave of dramatically more aggressive diplomacy by China since 2010 — fueled by a new sense of power from China’s rising economy and military.

Last year, glimmers of hope briefly appeared when a rare candidate acceptable to both Beijing and Rome was ordained in Shanghai. But those hopes were dashed after Bishop Thaddeus Ma Daqin stunned hundreds by abruptly announcing at his ordination that he was dropping out of the state church. His words, captured on video, were met with applause from the audience.

Soon after, he was detained by authorities and stripped of his title.

Encouraging signs

Catholics on both sides continue to look for encouraging signs. Many point to a recent article by a high-ranking Vatican cardinal as a clear indication that Rome wants to reengage. Acknowledging recent “misunderstandings [and] accusations,” Cardinal Fernando Filoni called for the creation of a bilateral commission to restart dialogue.

The next move, many believe, is China’s.

“The Vatican must always open the door to China,” because it is the pope’s job to care for his church, said Wang Meixiu, an expert in Catholicism at a government-sponsored think tank. But China’s attitude toward the Vatican is complicated by a multitude of internal and external factors.

In the midst of a sensitive leadership change, China’s government has toed its conventional line. China’s Foreign Ministry spokesman last week expressed hope that the new pope would “create conditions for improvement of bilateral relations,” which he suggested would require concessions from Rome.

But that has not dimmed hopes.

“As Catholics, we’re trained to be optimistic,” said Anthony Lam, a researcher under the Vatican’s Hong Kong Diocese. “For more than 2,000 years, the church has survived all manner of difficulty, from the Roman Empire to modern ones. We live in hope.”

Zhang Jie in Beijing contributed to this report.