The danger is that India and Pakistan think they could survive a nuclear war

After a week of hearing such views, I have dreams of taking over a TV station and playing tapes of Hiroshima over and over

Nations have gone to war over a great deal less, but seldom have they had so much to lose. A fairly self-evident thought, I admit, but after 15 hours in the heat and dust of the frontline it was as close to analytical perspicacity as I could manage. Just after midday we checked the temperature. It was climbing above 40. A Pakistani colonel pointed to the Indian watchtower across the fields. The Indians could see us, but they would not fire.

Nations have gone to war over a great deal less, but seldom have they had so much to lose. A fairly self-evident thought, I admit, but after 15 hours in the heat and dust of the frontline it was as close to analytical perspicacity as I could manage. Just after midday we checked the temperature. It was climbing above 40. A Pakistani colonel pointed to the Indian watchtower across the fields. The Indians could see us, but they would not fire.

A local reporter assured me that the Pakistani commander always radios his Indian counterpart when foreign journalists are coming to the front. Even while threatening each other's civilians with nuclear annihilation, the military men were touchingly preoccupied with our safety.

The front at Zafirwal faces on to Indian Jammu; on both sides of the line are millions of people living in desperate poverty. Superimposed on this tableau of civilian misery are nearly a million men at arms. The latter are well fed and sheltered. They fire salvoes of artillery shells while the civilians die, get wounded or flee.

An American television producer on the verge of collapse from heat exhaustion lurched towards the slender shade offered by the wall of an abandoned mosque. Gasping for breath, she wondered if any human being could fight a war in such heat. Our fixer Craig, a former soldier, thought it would be impossible. But he was applying the logic of distant Salisbury Plain, that is to say a certain cold logic. The calculations on the border of Indian-administered Kashmir are nothing like as clear-cut. The press pack in Pakistan, much like their colleagues on the other side of the border, spend hours discussing the what-ifs, but know as much as any informed person sitting in London. That is to say everybody is in the dark.

Islamabad before I left was a city of frantic whispers. The lobby of the Marriot Hotel hummed to the speculations of reporters from all over the world. Would India attack now, and were her armed forces ready? If they didn't attack now they would have to wait until after the monsoon rains. But no, they might just stage an aerial assault during the monsoon to catch Pakistan off guard. And so on. There were stories about secret meetings in Rawalpindi between the intelligence people and the militants, deals almost hammered out and then scuppered by a few recalcitrant groups, of Musharraf struggling to keep military hardliners on side, and the Americans drawing up plans to seize control of Pakistan's nuclear weapons.

Some of it is true and much of it is not. In an atmosphere where nothing is happening but London demands an update, the pages are cleared for the musings of men who might conceivably, perhaps, almost, nearly, plausibly have an insight to offer. It is rarely the case that they have. Old generals come out of retirement to hawk their warnings; they are little more than cheerleaders for muscular militarism, its hour come around at last.

The generals are in tune with the popular mood. Unlike Pakistan's sorry adventure in Afghanistan, this is an issue around which the nation has mobilised. Where only a fundamentalist minority really cared about the destruction of Mullah Omar's regime, there is a very different view of Kashmir. Actually, "view" is the wrong word. We are talking about a national obsession. It is not a question of how things are seen but of how they are felt. The mere mention of the word "India" induces an atavistic rage and no end of declarations that Pakistan must fight.

I went to a quarry outside Islamabad where men and boys earned £2.00 a day crushing and carrying stones. It is murderous work. At times you can hardly see the hunched figures through the clouds of dust. Most of the men are illiterate. They will earn barely enough to feed their families, and when they get too old or sick they can expect little support from the state. Nor can their children expect any improvement in their lives. The country is in the throes of economic crisis and things will not get better any time soon. But ask them if they resent the fact that Pakistan spends billions on nuclear weapons, and you get short shrift. Every single man I met thought the nukes were a good thing.

After a week of hearing views like this, I began to have daydreams about taking over the television station and playing tapes of Hiroshima and Nagasaki over and over. See how much dignity and national honour is left after the mushroom cloud and the firestorms and radiation. The poor men in the quarry would be vaporised by a bomb dropped on Islamabad. Their children's children would die from radiation sickness. The problem about nuclear war, all war for that matter, is that you have to go there to realise what a dumb idea it is. Can it be that in the last 48 hours this priceless truth has finally sunk in to the fevered brows in New Delhi and Islamabad?

Since leaving, I have followed the daily lack of developments with a morbid fascination and mounting apprehension. Up to a day ago I would have said a war was inevitable. But in the aftermath of the visit of the US envoy Richard Armitage, touted as Mr Bush's strong-arm man ( Time magazine tells us gushingly that he is a formidable weightlifter), the belligerents are sounding marginally less belligerent. And when you talk about nuclear war, margins really count.

The struggle between India and Pakistan has been with us for half a century, but the crisis over Kashmir in 2002 is one of those defining moments in human history. If either India or Pakistan opt to use nuclear weapons, they violate the taboo which has kept us safe from obliteration since 1945. The taboo against use of nuclear weapons is moral and practical. We believe that mass murder on such a scale is wrong, and likely to create a world in which there will be few survivors.

The danger with the India-Pakistan conflict is that the military planners on both sides believe loss of life will be great but not the mutually assured destruction that governed military calculations in the Cold War era. If they are proved right, then what would prevent other nuclear powers from using their weapons in future conflicts? Hard-headed military men across the world might learn the wrong lesson entirely: you can use a tactical nuclear weapon and kill millions, perhaps suffer a few million deaths yourself, but still survive as a viable state. Indeed, we have heard whispers from Delhi that India could absorb millions of casualties but still emerge victorious in a nuclear exchange.

War between India and Pakistan is a moment of choice for all humanity.

It threatens to take us into a new realm of what is plausible and acceptable in human relations. If needs be, President Bush and Tony Blair and Vladimir Putin and China's Jiang Zemin should do the unthinkable and go to the region together, bringing with them the concern of the world, but also a very definite warning: when nuclear war threatens, we are all threatened. This we cannot, must not and will not allow.

The writer is a BBC Special Correspondent