THERE was a time when Devon Chang had difficulty reconciling his two chosen faiths: Christianity, which he embraced in 2005 at the age of 19, and the Communist Party of China, which had embraced him a year earlier. Did his submission to an almighty God not mean he must renounce the godless club of Marx and Mao?

Not necessarily. A fellow convert's university lecturer suggested that if all Communist Party members found Jesus, then Christianity could rule China. “So it's a good thing for me to become a Christian,” Mr Chang reasoned.

The party does not quite see it that way. Although people join the party more for career reasons these days than for ideological ones, it still officially forbids religious belief among its members. In practice, this has for some years been a “don't ask, don't tell” policy. But signs are now growing that the party is about to become tougher on believers within its ranks. And behind it might be Mr Chang's notion of Christianity as a Trojan horse.

If you can't beat 'em…

Experts say that, of China's 1.3 billion people, 200m to 300m now practise religion (though the government admits to only 100m), and far more engage in the veneration of ancestors. The vast majority of the religious are Buddhists or Daoists. Estimates for the number of Christians vary wildly from 50m to 100m (they are hard to count because so many believers go to underground “house churches”). Across the country, local governments have rebuilt temples and constructed new ones to capitalise on religious tourism. In rural areas, temples and churches have helped provide education and health care, with the unofficial blessing of local party chiefs. Some of those leaders also act as temple chiefs.

In the absence of official figures on religious believers within the party, Western and Chinese scholars often quote a 2007 survey, carried out by Horizon, a Beijing polling firm, in co-operation with American academics. The poll found that one in six party members had a religious belief. This would equate to more than 13m members today. The vast majority of those are Buddhists. Close to 2m are Christians.

The signals of a harsher approach are coming from Zhu Weiqun, a deputy minister of the party's United Front Work Department and an influential ideologue, who warned in a December essay in a party journal, Qiushi (Seeking Truth), against the rise of religious believers in the ranks. If party members are allowed to believe in religion, Mr Zhu wrote, it will result in “shaking and losing the guiding position of Marxism, and in dividing the party ideologically and theoretically”. Mr Zhu cautioned that religious figures in the party might gain control over policy on religion. That would undermine the party's fight against religious “extremism” in China's west, especially against followers of the Dalai Lama. Mr Zhu is known as a loud public voice of the party's opposition to the exiled Tibetan leader, whom he has denounced as a “splittist”, who is “evil” and “deceitful”.

The party's relationship with religious believers who are not party members is complicated enough. They are allowed to believe in one of the state-approved religions (Buddhism, Daoism, Islam, as well as Protestant and Catholic Christianity) and to attend registered places of worship. In the countryside the party tolerates folk religion despite an official ban on superstitions. But recently the party has pursued a hard line against some old spiritual foes. The biggest concern is separatism, which the party fears is fuelled by Buddhism in Tibet, and Islam in the north-west. But underground Catholic churches that are loyal to the pope and some of the more confrontational Protestant house churches are also controlled tightly.

Perceived threats to social stability are provoking the party's soul-searching more than any need for thought control. The past four years have seen a succession of crises that have rejuvenated hardliners on the conservative wing of the party, where Mr Zhu resides, and where venom against religion is most in evidence. In the run-up to this autumn's transition of the party's top leaders, some officials are taking an even more conservative line as the safer path to power in nervous times.

During last year's Arab spring, online calls for a Chinese “jasmine revolution” triggered a tightening of control. Beijing's highest-profile house church, known as Shouwang, took what even many of its supporters felt was too confrontational a stand in a dispute about its venue and its leaders were detained. Other house churches that stay out of politics are still mostly left alone. But anything that smacks of civil society organising itself is considered suspect. The fact that few in China appeared to heed the call for an Egyptian-style revolt may have been taken as proof that harsh tactics work, not that they are unnecessary.

Even as greater prosperity and integration with the world transform Chinese society, the political climate is as icy as it has been since the early 1990s, when ageing hardliners criticised the role of religion in society. There was almost an opening a decade ago, when Pan Yue, a government official then handling economic reforms, published an article calling for a reassessment of the relationship between religion and the party. He argued that Marx was not as opposed to the “opium of the people” as is assumed, and that religion could help the party maintain stability. President Hu Jintao's predecessor, Jiang Zemin, appeared to accept that religion was a force that had a lasting place in Chinese society, and even dedicated a number of Buddhist temples with his calligraphy. But Mr Jiang kept party membership closed to believers, while admitting some of Marx's less spiritual enemies: the capitalists.

Other party leaders have also made public allowances for religion, as long as it stays within the broad tent of party control. Some even privately suggest that religious faith may bring ethical benefits in the widely lamented moral vacuum of rampant materialism. But that need for a new moral code is tempered by a continued suspicion, especially of a faith such as Christianity, which is still tainted by its historical links to foreign imperialism.

So for believers such as young Mr Chang, the convert in Beijing, some tensions remain. He says he joined the party at the behest of his parents (his father is a member), because it would help him find a job. But his lack of party connections hindered his job search. God, he says, answered his prayers instead. Now he works for a government ministry, but he cannot tell his co-workers about his faith or he will be fired. He says he wants to leave his job, despite objections from his parents, who argue that success within the party can help the family more than God can.

Mr Chang and two other party members who attend the same church in Beijing insist the two faiths can co-exist. The country needs the party, they say, whereas individuals need faith. Christian party members note what Jesus taught his followers: “Render unto Caesar the things which are Caesar's, and unto God the things that are God's.”. Mr Chang's party dues are $1.60 a month. He plans to keep paying them.