THE BUSH administration is known for gambles, and Monday's about-face on nuclear cooperation with India qualifies as such. By declaring that it would help India build nuclear power plants and import advanced weapons, the administration has made good on its statement that it wants India to become "a major world power in the 21st century." But it has simultaneously set aside the principle that countries refusing to sign the nuclear Non-Proliferation Treaty should be denied civilian nuclear assistance and, in many cases, face a weapons embargo. The gains from this shift could be considerable, but so too could the risks. Much will depend on the administration's skill in assembling support for its new stance, in Congress and internationally.

Start with the potential benefits. India, with a population of just over 1 billion, is already the biggest democracy in the world and will eventually overtake China as the most populous of all nations. Its economy has grown rapidly in the past decade, and it has become a global player in software, computer services and pharmaceuticals. As an emerging Asian superpower, India may serve as a counterweight to China. As home to a large and tolerant Muslim population, it may serve as an ally against Islamic militancy. The standoff over India's nuclear policy, which grew serious when India tested nuclear weapons in 1998, has been an obstacle to closer ties with this dynamic and like-minded democracy. Understandably, the administration wants to address that.

It's fair to ask what "closer ties" may mean in practice. Although India's rising power may constrain China in a general way, India does not share the U.S. commitment to defend Taiwan and would probably stand aside in other potential U.S.-China rows that do not affect Indian interests. Equally, cooperation on terrorism or economic relations will take place when it suits the interests of both countries and not otherwise. India's noisy democracy tends to feature coalition governments that include anti-American voices, just as America's noisy democracy features protectionist members of Congress who blame India for the loss of U.S. jobs. So the Bush administration is right to want close ties with India, but these will have limits.

India does promise some concrete concessions in return for nuclear cooperation. It will commit itself to abstain from further nuclear tests, to open its civilian nuclear reactors to international inspections, and to withhold nuclear technology or material from illegal proliferators. The importance of these promises is qualified by the fact that India had already chosen unilaterally to forgo nuclear tests and to safeguard its nuclear material. But the Bush administration, which has sometimes argued that treaties and protocols don't reliably constrain national behavior and are therefore of limited worth, rightly sees some value in converting India's voluntary good behavior on nuclear proliferation into a more formal obligation.

Now consider the risks in the administration's gamble. Pakistan, India's neighbor and rival, will seek a similar de facto blessing for its nuclear status. Given Pakistan's record as a nuclear proliferator, the United States ought to refuse this. A rebuff could help to turn Pakistan's anti-Indian nationalism into an anti-India-and-America nationalism; pro-Western secularists may lose ground to militant Islamists. If so, the upside of a stronger relationship with India will have to be weighed against the potential downside of a jihad-minded nuclear Pakistan.

The administration's efforts to contain the nuclearization of Iran and North Korea may also suffer. Help in building civilian nuclear reactors is a carrot for countries that agree not to build nuclear weapons. If India can build such weapons and then munch the carrot anyway, why should others not aim to do likewise?

The Bush administration can answer that India has earned its exceptional status. Unlike Iran and North Korea, India was never a signatory to the Non-Proliferation Treaty and therefore never broke its word; unlike Pakistan, it has not sold its nuclear secrets to others. But this argument may not prevent other nuclear powers from asserting exceptional status for their own friends. Russia may sell more weapons to Iran. China may refuse to get tough on North Korea. Both of these bad outcomes seemed probable anyway, but the administration's new stance has made them likelier.

Monday's U.S.-India communique is only a declaration of intent. To clear the way for U.S. assistance to India's civilian nuclear program, the administration will have to ask Congress for legislation. To salvage something of the nonproliferation regime, the administration will need buy-in from other nuclear powers. In both cases, the administration will need to convince a skeptical audience that the gains from its proposal outweigh the risks. As the Bush team has discovered before, announcing a bold new policy is easier than implementing it.