The United States and India have put aside their troubled past to reach far into the future with a visionary bilateral agreement that challenges both nations and the rest of the world to treat nuclear weapons and nuclear energy with greater realism than they do under the nuclear Non-Proliferation Treaty.

If Congress agrees to the changes in law sought by the Bush administration to put the agreement signed last week into force, nuclear energy will take center stage from nuclear weapons in the new order of U.S.-Indian relations, which now become crucial to constructing a post-Kyoto consensus on climate change.

Energy vs. arms has been an atomic trade-off dictated by the nuclear treaty for nearly a half-century -- before global warming became a major international concern, and before rogue states showed they were not interested in such a trade.

New Delhi and Washington give impetus both to the growing acceptance by environmentalists of nuclear energy as a lesser evil and to the Bush Doctrine of post-Sept. 11 security.

The odd status of nuclear energy as a combination risk (at least since the Three Mile Island disaster in 1979) and reward (for developing countries) mutates as fossil fuel pollution becomes a greater threat. For differing reasons, the United States, India and China are outside the restrictions of the Kyoto Protocol. Until that changes, a global climate change system will not work.

For the Bush administration, this accord demonstrates the peaceful application of a national security strategy that holds that the nature of regimes, rather than the nature of the weapons they possess, will determine their relations with Washington.

This is the first important diplomatic accomplishment of the George W. Bush presidency, which was as bare as Old Mother Hubbard's cupboard in its first four years. President Bush needs to do much more to become convincing on both nuclear strategy and climate change. But it is important to recognize that his second-term team has put into place a cornerstone for far-reaching change -- and did so while resisting India's demands for formal recognition as a nuclear weapons state.

Not everyone will think that is progress. Viewed from the peculiar and selective morality embodied in the nuclear treaty, the United States has now surrendered both the moral and practical high grounds by agreeing to support India's right to buy and develop the reactors, fuel and technology it needs for an effective national nuclear energy program.

The Non-Proliferation Treaty, which took effect in 1970, offers such advantages only to states that do not develop nuclear weapons, which India did in 1974. Along with effective diplomatic pressure from the United States and the nuclear suppliers cartel, the treaty has helped delay or prevent a number of other states from acquiring nuclear arsenals.

But the pact was based on a fiction that was temporarily useful. The five declared nuclear states of 1970 granted legitimacy to their arsenals in return for pledging insincerely "to pursue good-faith negotiations" to abolish them. Washington, London, Paris, Moscow and Beijing intended to maintain the code of the nuclear priesthood on their own terms, as India pointed out in refusing to sign the treaty. That approach has been overtaken by the ability of other states to make nuclear weapons without the help or permission of the Big Five.

Instead of making the treaty's shortcomings the issue, as Bush did with Kyoto and with the Anti-Ballistic Missile Treaty with Russia, which he abrogated, the president has simply placed the Indian-U.S. relationship outside the treaty's most restrictive conditions. This is realism of a high order, particularly for a president often accused of lacking realism in his foreign policy.

Bush accepts the premise that the world's largest democracy has nuclear weapons and technology that it does not intend to use against U.S. interests. The United States has long tolerated Israel's nuclear arsenal on the same basis and can reasonably oppose the programs of the hostile regimes of Iran and North Korea by the same standards. Pakistan occupies a difficult, and highly dangerous, middle ground for U.S. interests.

Little in life is as theoretical as the overdrawn discussion of the importance of realism and idealism in shaping U.S. foreign policy. All administrations apply a mixture of both that is determined as often by unexpected events abroad and political pressures at home as by grand, fixed designs. What is described as "realism" is frequently pure cynicism in semantic disguise, while "idealism" can be grievous misjudgment dressed up as good intentions. See Chile, 1973, as an example of the first tendency; Iraq today of the second.

The real dividing line in charting policy is between optimists and pessimists. Those are the qualities that determine which bets get made and which are shunned. In dealing with India as it is, and for the potential it holds, Bush shows again that he is first and foremost a historical optimist who bets big and bold.