However, less obvious pressures are also undermining nuclear arms control as both big and emerging powers seek strategic and commercial gains. China is planning to provide more nuclear power reactors and fuel to Pakistan, even though Pakistan refuses to join the NPT and accept rigorous IAEA surveillance of all its nuclear facilities. In a clear sign that the deal will proceed, two Chinese state-owned companies last month signed a contract to cooperate in building the reactors to generate electricity at Pakistan's Chasma atomic complex, advancing a program that worries the United States and India.

Washington and New Delhi can hardly be surprised. Their own agreement in 2005 to reopen civilian nuclear trade blew a hole in international arrangements to stop proliferation. The agreement with the U.S. was sealed despite India's nuclear weapons tests in 1998, which triggered follow-on tests by its longtime rival Pakistan.

A key part of the counter-proliferation system is the Nuclear Suppliers Group (NSG) of 46 participating governments that between them control much of the knowhow, equipment and material needed for both civilian and military nuclear programs. They regulate the most powerful technology and fissile materials so far developed. Australia, which has about 40 percent of the world's commercially recoverable uranium resources, is a member of the informal cartel.

The NSG was established in 1975 to reinforce the NPT. Its voluntary guidelines were designed to prevent the transfer of sensitive nuclear technologies and block nuclear commerce with states that did not observe basic nonproliferation standards. The NSG barred trade with non-NPT countries. India was one of only three states never to have signed the treaty. The others were Pakistan and Israel.

Yet in 2001, Russia, a prominent NSG member, sold uranium to India and agreed to build two additional reactors for India, without NSG approval.

Under U.S. pressure, but with strong backing from Russia, France and Britain, the NSG agreed in 2008 to exempt nuclear transfers to India. All India's backers sought closer ties with South Asia's leading power and wanted to cash in on India's expansion of its civilian nuclear power market worth about $150 billion.

At least India had no record of transferring its nuclear knowhow abroad. Pakistan has been the source of clandestine nuclear weapons and missile technology transfers to North Korea, Iran and Libya. It is expanding its capacity to produce plutonium and highly enriched uranium for weapons and has blocked the start of international negotiations on a treaty to ban production of fissile material for nuclear arms.

Yet since the NSG exemption granted to India, China has been seeking equal treatment for its ally Pakistan so that it can expand civilian nuclear power. Israel, too, has sought exemption. Both moves have been unsuccessful.

When China joined the NSG in 2004, it had already built a power reactor at Pakistan's Chasma site. Beijing said at the time it was entitled to build a second reactor because it was part of the original agreement with Islamabad. However, building a third and fourth reactors, as China plans to do, would be another major breach in NSG standards.

Even Japan, the only country to have suffered a nuclear attack, may be ready to bend its strict controls on nuclear exports. Japan and India held their first round of negotiations on a civilian nuclear pact at the end of last month.

As the nuclear power industry expands, particularly in Asia, Japan wants to compete with China and South Korea in lucrative nuclear exports. It is also under pressure from the U.S. and European countries whose nuclear companies have formed joint ventures with Japanese firms that are circumscribed by Tokyo's strict compliance with the NPT and NSG guidelines.

Hinting at new flexibility, Japan's trade minister, Masayuki Naoshima, said recently that India's use of nuclear technology for peaceful purposes "has already been internationally accepted." The U.S., Russia, France and Canada have already signed nuclear cooperation agreements with India.

Australia has yet to indicate whether it, too, will shift ground and lift its ban on selling uranium to India.

At a meeting of the NSG in New Zealand last month, China sidestepped questions about its plan to sell Pakistan two additional reactors. The meeting also failed to agree on tougher guidelines on transfer of uranium enrichment and spent fuel reprocessing technology.

Some emerging powers that are NSG members, including Brazil, South Africa and Turkey, fear that U.N. Security Council sanctions imposed on Iran by the U.S., Russia, China, France and Britain — the five big nuclear powers — may make it more difficult in future for them to enrich their own uranium for energy security and export.

More than 30 countries are planning to start nuclear power programs, doubling the number that already do so. Many are in Asia, the Middle East, South America and Africa.

Without strict international rules on nuclear trade, the technologies and materials that can be used to make weapons of mass destruction will become more widely available, triggering regional nuclear arms races and opening the door for terrorists to get the ultimate weapons of fear and blackmail.