INDIA refused to accede to the Comprehensive Test Ban Treaty (CTBT) when it was negotiated in 1996 because it sought to pressure the nuclear weapons states into achieving complete nuclear disarmament. But no one paid much attention. That reality changed with the May nuclear tests which established India as a nuclear weapons state. The nuclear attention-deficit-disorder disappeared. It has been a demonstration of the depravity of world politics that an India that exercised restraint and advocated disarmament was brushed aside, while a nuclear-armed India is taken more seriously. But this political authority in the world of realpolitik has come at a price. For alongside India has also lost the moral authority and the leadership of the non-aligned movement from which to mobilise world opinion for disarmament. The slow erosion of that leadership since the 1974 test is now complete. That inconvenient reality has not yet been acknowledged by India, but it is an unavoidable consequence of the tests. Right Direction The opportunities for India are now radically different. The CTBT is one of two critical areas where the country faces crucial nuclear choices. The other is weaponisation: Will India arm its delivery vehicles? In both areas, India's decisions will profoundly affect the future of the country and could help shape the future of the world. In both cases, India's initial steps have been in the right direction. India has declared a unilateral moratorium on nuclear testing and, by all accounts, decided, at least for the moment, not to arm its delivery vehicles. But these steps are too small to register on the scale of world politics or to re-establish India's moral leadership after its decision to test nuclear weapons. The CTBT presents India with a highly unusual opportunity for re-establishing disarmament leadership in a powerful way. The United States and France are building facilities that are designed to create thermonuclear (i.e., fusion) explosions ignited by huge lasers. Research done at my institute (by my colleague Hisham Zerriffi and myself) shows that these facilities are illegal under the CTBT, which bans all nuclear explosions. In fact, even building them violates the CTBT, which requires parties to prevent nuclear explosions, in direct contradiction to the US and French plans. While the CTBT does not define a nuclear explosion, the negotiating record clearly indicates that a fission explosion of more than four pounds of TNT equivalent, and even far less, would be banned. That is the meaning of a "zero yield" treaty to which the United States, France and other nuclear weapons signatory states gave their explicit assent. If pure thermonuclear explosions greater than four pounds of TNT equivalent were allowed, there would be no effective upper limit to them. Indeed, the CTBT would become meaningless. If ten pound explosions are to be allowed, why not one hundred pound or ten thousand pound TNT equivalent explosions? The huge lasers being built in the United States and France cannot be miniaturized into triggers for pure fusion weapons -- hydrogen bombs that require no plutonium or uranium. But, if they work as their designers hope, they would establish the scientific feasibility of the concept. A number of US scientific authorities, including Nobel Prize winner Hans Bethe, have already expressed serious concerns about the fusion weapons possibility. Such bombs could be made in sizes ranging from small to huge and would produce little or no radioactive fallout. As a result, militaries would be far more inclined to use them in battlefield situations. Tool for Disarmament Given the continued political weakness of the position of non-nuclear-weapons states on nuclear disarmament, no country is now taking the leadership to establish an official definition of nuclear explosions or to seek an official opinion regarding the legality of the US and French laser fusion facilities. The door is wide open for India. But to seize the moment, India must not only sign and ratify the CTBT, it must also unilaterally renounce the design of new nuclear weapons and the use of a "stockpile stewardship" or any other programme for that purpose. Only on that basis could India effectively call for a halt to the construction of the US and French facilities and for all countries to work to convert the CTBT from being mainly an instrument of non-proliferation policy into a tool for nuclear disarmament. Will India choose leadership of the global disarmament movement and help raise the CTBT to its historic disarmament purpose, a dream first dreamed by India for which it is still deeply respected by the world's people? The writer is president of the Institute for Energy and Environmental Research in Takoma Park, Maryland.