AT FIRST sight, China's proposed sale of two civilian nuclear-power reactors to Pakistan hardly seems a danger sign. Pakistan already has the bomb, so it has all the nuclear secrets it needs. Next-door India has the bomb too, and has been seeking similar deals with other countries.

Yet the sale (really a gift, as Pakistan is broke) has caused shudders at the Nuclear Suppliers Group (NSG), an informal cartel of countries who want to stop their advanced nuclear technology getting into the wrong hands. They are meeting in New Zealand, for what was supposed to be a quiet and nerdish rule-tightening session. But their efforts may now fall victim to China's rivalry with America.

By any measure, Pakistan is a shocker. Its proliferation record would make the serial nuclear mischief-makers of North Korea blush. If the Chinese reactor deal goes ahead, the damage will be huge: beyond just stoking the already alarming nuclear rivalry between Pakistan and India.

That does not deter China, which still seethes about the way in which the Bush administration in 2008 browbeat other NSG members into exempting America's friend India from the group's rules. These banned nuclear trade, even civilian deals, with countries like India and Pakistan, but also Israel and now North Korea, that resist full international safeguards on all their nuclear industry.

America argued that India had a spotless non-proliferation record (it doesn't) and that bringing it into the non-proliferation “mainstream” could only bolster global anti-proliferation efforts (it didn't). The deal incensed not just China and Pakistan but many others, inside and outside the NSG. An immediate casualty was the effort to get all members of the Nuclear Non-Proliferation Treaty (NPT), who have already promised not to seek the bomb, to sign up to an additional protocol on toughened safeguards. Many have, but on hearing of the America-India deal Brazil's president is reputed to have flatly ruled that out. And where Brazil has put its foot down, others have also hesitated.

What particularly riles outsiders is that America did not get anything much out of India in return. It did not win backing for new anti-proliferation obligations, such as a legally binding test ban or for an end to the further production of fissile uranium or plutonium for bombs. India has since designated some of its reactors as civilian, and open to inspection, but others still churn out spent fuel richly laden with weapons-usable plutonium. India can potentially make even more of the stuff. Now that it can import uranium fuel for its civilian reactors, it can devote more of its scarce domestic supplies to bomb-making.

Pakistan suffers no such uranium shortage and is determined to match India. According to analysis of satellite imagery by the Washington-based Institute for Science and International Security, it is greatly expanding its capacity to produce weapons-usable plutonium, as well as uranium.

China has given Pakistan lots of nuclear and missile help in the past. It even passed it a tested design of one of its own missile-mountable warheads. This was one of the most damaging proliferation acts of the nuclear age, since the same design was later passed by Pakistan to Libya and possibly Iran and others.

But after China joined the NPT in 1992 and the NSG in 2004, it reined in such help, at least officially (some Chinese firms are still involved in illicit nuclear trade with several states). But on joining the NSG, it argued that it had already promised to build the second of two nuclear reactors for Pakistan at Chasma in Punjab and would therefore go ahead. Some grumbled. But it seemed a price worth paying to have China inside, playing by the NSG's rules rather than outside, undermining them. The latest sale blows a hole in that hope.

A big leaky tent

China is trying a legalistic defence of the sale of the third and fourth reactors at Chasma. But its real point is this: if America can bend the rules for India, then China can break them for Pakistan.

Pakistan hopes that it will eventually get a deal like India's. Some in Barack Obama's administration have supported this, on the ground that America needs Pakistan's support in the fight against al-Qaeda and the Taleban. Israel wouldn't mind such an exemption either.

The NSG's damage-control efforts now centre on a new rule to bar the sale of kit for uranium-enrichment or plutonium-reprocessing to any country outside the NPT. That, predictably, annoys India.

The deal also affects efforts to contain Iran. Western diplomats seeking support for UN sanctions on the Islamic republic find themselves receiving a wigging over the double standards used with India. Iranian officials used to argue that they just wanted to be treated like Japan. It has free access to advanced nuclear technology. But unlike Iran, Japan does not repeatedly violate nuclear safeguards. Some Iranian officials now muse boldly that the big powers will eventually come to do deals with them, just as they did with India. Iran's latest raspberry in response to a fourth round of UN sanctions was to ban two nuclear inspectors from the International Atomic Energy Agency, the UN's nuclear guardian. Iran dislikes its reports on the regime's dubious nuclear activities.

If Pakistan really is worried about India's growing nuclear arsenal, diplomacy might work better than an arms race. George Perkovich of the Carnegie Endowment, a think tank, says Pakistan should lift its veto on a ban on the production of fissile materials for bombs. That would put India (which claims to support a ban) on the spot. Like enriched uranium, hypocrisy can be costlier than it seems.