It would not mean the end of the nuclear age, still less the dawn of eternal peace. More than 16,000 nuclear warheads, capable of delivery by intercontinental missile or bomber aircraft, remain, largely in the hands of the United States and Russia.
Apart from these, the nuclear powers possess more than 10,000 short-range and other warheads. Put more starkly, the total yield of all the world's nuclear weapons is sufficient to cause more than 300,000 Hiroshima-style explosions.
Nuclear deterrence, nuclear proliferation, nuclear madness - all these concepts will remain with us, whether or not the test ban goes ahead. Yet a ban on tests would represent a considerable achievement on a planet that has shuddered more than 2,000 times since the end of the Second World War from the impact of nuclear weapons explosions in the atmosphere, underground and in the water.
Most countries attending the Geneva talks on a Comprehensive Test Ban Treaty (CTBT) support the proposal to stop tests. Crucially, these include the five declared nuclear powers - Britain, China, France, Russia and the United States. All have now stopped testing, China last month and France earlier this year after a series of tests in the South Pacific that outraged world opinion.
Despite problems with Iran and Cuba, the main threat to the treaty comes from India, the only country openly opposing it in its present form. Along with Israel and Pakistan, India is a "threshold" nuclear power - a state that has nuclear weapons but does not admit it, or has enough fissile materials to build such weapons at short notice.
Some diplomats say that if India does not lift its objections, the question will remain whether the treaty is anything other than a piece of paper inscribed with noble intentions. It could still go forward next month to the United Nations in New York, where member-states would be invited to ratify it, but India's refusal to endorse the document could tempt some countries to regard it as a pious and irrelevant proclamation.
"India is running the risk of taking the full blame if the talks fail," a Western diplomat in Geneva said. "Everyone else realises this is the right treaty."
Ironically, India's first post-independence prime minister, Jawaharlal Nehru, was among the earliest advocates of a test ban, making the proposal in 1954 as a way of halting the Cold War arms race. For India, the picture changed completely 10 years later, when its giant neighbour and rival, China, exploded its first nuclear weapon at Lop Nor.
In 1974, India conducted a nuclear test of its own. It has always described this as an explosion of a "peaceful nuclear device", but no one - least of all China and Pakistan, India's second great adversary - doubts that the test was a milestone on India's path to undeclared nuclear status.
India's objections to the CTBT are many and varied. One is that, unless the treaty is linked to a timetable for global nuclear disarmament, it will merely confirm the privileged position of the five declared nuclear powers.
From an Indian perspective, the willingness of these countries to abandon nuclear tests reeks of hypocrisy, since technological advances mean that they are all capable of simulating tests in laboratories. Declaring a test ban in these circumstances is, say the Indians, a little like locking the stable door after the nuclear horse has bolted.
The Indian government is also resisting a provision of the treaty that requires the five nuclear powers and India, Israel and Pakistan to ratify the pact before it becomes international law. The thinking behind this clause is simple: if a "threshold" power such as India does not sign the treaty, then other countries that may aspire to nuclear status will have a perfect excuse not to sign either.
India contends, however, that the requirement encroaches on its sovereign right to decide freely what international agreements it wishes to enter into. Last week the Indian representative in Geneva, Arundhati Ghose, proposed an amendment under which the treaty would take effect only after ratification by 65 states.
India's fundamental objection is that, if it were to ratify the treaty as it stands now, it would be tying one hand behind its back before any future conflict with China or Pakistan. The suspicions and fears that infect relations between India and its two neighbours may, in the end, prove the downfall of the CTBT.
Having fought three wars with Pakistan since independence in 1947, India is constantly on the watch for some treacherous Pakistani move against Indian territory. It does not help that the Indian government is battling to put down a separatist revolt in the two-thirds of Kashmir that lies inside India's borders.
Although India's population of 850 million outnumbers that of Pakistan by a factor of about seven to one, the sense of a threat is ever-present, enhanced by the awareness that Pakistan is an undeclared nuclear power. Yet the biggest problem for India lies not in Pakistan but in China, an even more populous country than India and one that has conducted about 45 nuclear tests - the last of which occurred on 29 July, the very day that the Geneva talks reopened after a month's recess.
"Pakistan isn't the top worry for India. For them, China is always top of the list," said Bates Gill, an analyst at the Stockholm International Peace Research Institute.
China fought a brief border war with India in 1962 and, partly on the principle that your enemy's enemy is your friend, has maintained a long- standing military relationship with Pakistan. Both the Chinese and Pakistanis have denied Western press reports that China has supplied Pakistan with M-11 missiles for delivering nuclear warheads, but India continues to view the Chinese-Pakistani alliance with apprehension.
It is a measure of the depth of India's security concerns that the main opposition party, the right-wing Hindu Bharatiya Janata Party (BJP), openly supports the deployment of nuclear weapons at a time when the rest of the world claims to want to move in completely the other direction. The BJP's foreign affairs spokesman, Brijesh Mishra, went further last week and said: "We must conduct one or more nuclear tests in order to design nuclear warheads for our missiles."
In addition, Indian newspapers reported last Friday that the state-run Defence Research and Development Organisation had proposed to the government that tests of a controversial intermediate-range missile, the Agni, should be resumed. The Agni, which is named after the Hindu fire god, has been tested twice before, the last time in February 1994, but India has come under US pressure to drop the programme on the grounds that it raises tensions with China and Pakistan.
For some while after the CTBT negotiations began in January 1994, it appeared that China might prove as big an obstacle as India to a complete test ban. The Chinese were particularly opposed to a proposal, advanced by the US, that information gathered from satellites and other forms of technical intelligence should be used as the basis for making a request for "on-site inspections" of nuclear facilities.
Essentially, the Chinese viewed this proposal as a licence for espionage. They also argued that inspections should not go ahead unless a two-thirds majority of the treaty's 51-nation executive council voted for them, whereas the US said that a simple majority vote should suffice.
Last week, in one of the major breakthroughs of the talks, the US and China reached a compromise. The US agreed that the number of votes required to trigger an inspection should be raised to 30, while China undertook to use its influence on Pakistan to make it sign the CTBT.
The US also appears to have assured China that it will not use information acquired by spying to demand inspections. In return, the Chinese promised that, should India refuse to endorse the treaty, they will still co-operate with US efforts to send the document to the UN General Assembly for signing.
This compromise makes clear that the US sees value in adopting the treaty even without Indian approval. The reason is that if, after three years, the treaty has still not come into effect because of Indian opposition, a new conference can be held to decide on measures to accelerate the ratification process.
This clause could be interpreted to mean that the treaty, far from being buried because of Indian objections, has "provisional application". Those states that sign the treaty will be bound never to conduct a nuclear test, while those that do not sign will be under extreme pressure not to carry out a test because the weight of international opinion will be overwhelmingly against them.
Officials in New Delhi have expressed concern that the US and other powers might attempt to use the conference three years from now to impose economic sanctions on India for not ratifying the CTBT. However, the US Secretary of State, Warren Christopher, wrote a letter to the Indian government pledging that the US had no intention of penalising India in this fashion.
Another way of saving the treaty, if India refuses to approve it, is to omit the names of the eight countries whose ratification is needed to make it operative. However, India may not regard such a step as meeting its substantive objections.
As a former Indian foreign minister, AP Venkateswaran, indicated, India's worries about China and Pakistan are so profound that it is ready to endure isolation as the price of rejecting the treaty. "It is better to die on your feet than to live on your knees," he said.
The Geneva talks are so tantalisingly close to success that it seems unlikely that the US and the other four declared nuclear powers will let them break down completely. Yet it cannot be stressed too often that the CTBT is not an act of nuclear disarmament and may not even serve as an incentive to disarmament.
Perhaps the most telling episode at the Geneva talks happened last Thursday, when 29 developing countries proposed immediate negotiations on a timetable for destroying nuclear arsenals by 2020. The proposal was dismissed as wildly utopian by the chief US delegate, Stephen Ledogar, who called it a "long, complicated wish-list that would amount to all nuclear weapons states being required to ... destroy in accordance with a timetable dictated by others. That is simply not in the cards for the United States, or indeed for any of the other nuclear weapons states."