Very Thin Red Lines : As India and Pakistan teeter close to war, no one knows what they'll do with their nukes.(Illustration)

In most conflicts, the "fog of war" settles in after the shooting starts. Not so in strife-torn Kashmir. There, on what might well become a nuclear battlefield, India and Pakistan know the least about their most devastating weapons. Neither side really knows how many nuclear warheads the other has. Neither is sure how the other plans to deliver those weapons--or under what circumstances. To this day there are conflicting accounts of how many nuclear tests each country staged in 1998, when they sought to outdo each other with displays of martial prowess.

Those unknowns have taken on terrifying implications. Nearly a million troops have eyeballed each other across the Line of Control dividing them since January, when New Delhi threatened to retaliate for a suicide attack on the Indian Parliament by militants allegedly linked to Pakistan. Ever since another attack on an Army base in Kashmir on May 14, India has trumpeted its preparations for war: fighter squadrons and large artillery batteries have been moved to forward bases in Kashmir, warships are steaming toward the Pakistani coast, troops and supplies have been rushed north. Last week Indian Prime Minister Atal Bihari Vajpayee told troops along the Line of Control to prepare for a "decisive battle." The critical question is the nukes--if and when and how they will be used. The fact that neither side has an answer is what makes this conflict truly the most dangerous in the world.

Uncertainty over the nukes is key to India's decision whether to attack or not. Until now the possibility that any military confrontation could quickly escalate has restrained both sides; Indian saber-rattling has generally been meant to push the United States to extract concessions from the Pakistani president, Gen. Pervez Musharraf, its ally in the war on terror. (Even now many observers think India will not launch an attack while high-level envoys--including British Foreign Minister Jack Straw and U.S. Deputy Secretary of State Richard Armitage--are headed to the region.) But for the first time, say both Indian and Pakistani officials, New Delhi seems confident that a limited conventional attack--most likely a combined air and ground assault on alleged terrorist camps in Pakistan- controlled Kashmir--will provoke only a limited response. "Unless there's a really high-profile attack [by India] and an absolutely dramatic collapse," Pakistan would probably not resort to its nuclear weapons, says Robert Bradnock, director of the Geopolitics Research Centre at the School of Oriental and African Studies in London.

The problem with this logic is that India's war aims also remain opaque. The strategic balance in South Asia has for years relied on what analysts call "ugly stability": the threat of nuclear weapons has enforced calm between India and Pakistan, while allowing low-level violence to fester. Now, however, New Delhi may be looking to alter the paradigm. "Provocations that originate on the Pakistani side of the Kashmir divide... are [traditionally] not responded to in kind by the Indian armed forces," says Michael Krepon, an expert on South Asian security issues at the Stimson Center in Washington, who just returned from meetings with senior Indian officials. "My sense is that violence across the Line of Control henceforth will be a two-way street." U.S. officials agree that Indian military strategists are likely aiming higher than ever before-- laying plans not only to destroy training camps, but to take and hold the mountain passes through which insurgents enter Kashmir, and even possibly push far enough north to control the Indus River watershed that supplies Pakistan.

Whether such an attack would provoke a nuclear response is unclear, precisely because both India and Pakistan have never laid out where their so-called "red lines"--the triggers for a nuclear retaliation--are. Islamabad describes its tipping point as a looming collapse in the face of an Indian conventional or nuclear attack: "If Pakistan's existence is threatened, it will use nuclear weapons," the Communications minister, retired Lt. Gen. Javed Ashraf, said last week. India has always said it would use its nukes only in self-defense. But even that position is fuzzy. A quasi-official 1999 paper on the country's nuclear doctrine says that "any threat of use of nuclear weapons against India shall invoke measures to counter the threat." Conceivably that could justify pre-emptive strikes against Pakistan's nuclear arsenal or ...