HONOLULU -- The handshake between Indian Prime Minister Atal Behari Vajpayee and Pakistani President Pervez Musharraf in Nepal last Saturday caused an international sigh of relief as the two nuclear powers took a tentative step back from the brink of war. Tensions will remain high on the Indian subcontinent, however, as New Delhi waits to see if Islamabad follows through with its current crackdown on Kashmiri terrorist camps and havens in Pakistan.

But those worrying about a deliberate nuclear war between these two historic rivals are missing the real danger. Even if Indian decides to launch surgical strikes against terrorist camps in Pakistan, and even if Pakistan retaliates (and China rattles its sabers in support), the odds are extremely high that neither leader would resort to the use of his limited nuclear arsenal; Vajpayee because he doesn't have to and Musharraf because the arsenal represents his major ace in the hole, to be saved until national survival is truly at risk.

Nor is there much danger of Musharraf playing his "China card." Although Pakistani leader made a point of traveling to Katmandu via Beijing, where Chinese Premier Zhu Rongji expressed China's steadfast support for Pakistan, China's last attempt to "teach a lesson" to one of its neighbors for attacking one of its friends -- its brief but bloody invasion into northern Vietnam in 1979 -- will likely cause it to think twice before reacting against a much more capable foe, especially if India's objectives are limited to terrorist targets.

All of this is not to dismiss either the likelihood or seriousness of a new Indo-Pakistani clash. It would be extremely deadly and have the added consequence of detracting from the U.S.-led war against the terrorists of choice, Osama bin Laden's al-Qaeda network. The real danger is the growing international acceptance of India and Pakistan as ex-officio members of the nuclear weapons club and what this means as they both proceed down the nuclear weapons path.

I would agree (somewhat begrudgingly) that the politically expedient lifting of the remaining sanctions imposed by the U.S. after India and Pakistan came out of the nuclear closet with their 1998 tests made sense, given both their general ineffectiveness (few others supported this U.S. effort) and the need to have both states (and especially Pakistan) firmly in the U.S. antiterrorist camp. I also concede that it would be virtually impossible today to convince either country to put its nuclear genie back in the bottle.

Yet going back to "business as usual" -- as India arrogantly but rightly predicted we would when confronting the initial international uproar after its 1998 tests -- neglects the real dangers that lie ahead if either country takes the next logical (or, in my view, illogical) step -- namely, the operational field deployment of its nuclear weapons.

If either side deploys nuclear warhead-equipped missiles in the field (and India seems determined to pursue this course), the other will almost automatically follow suit. This will greatly increase the danger of inadvertent or unauthorized use, while encouraging pre-emptive strikes and a "use or lose" philosophy that would "justify" a nuclear response to a conventional attack (or perhaps even threat of imminent attack) against the other's field-deployed sites.

And, while one assumes that both sides' nuclear warheads are tightly guarded today, deploying them to the field makes them that much more vulnerable to seizure by terrorists or even by renegade national forces.

In truth, the U.S. is today talking about going beyond "business as usual" to establish a deeper military-to-military relationship with India, to include the initiation of arms sales, something Washington has resisted doing in the past. Yet there is little talk of strings being attached to this increased cooperation. At a minimum, Washington should seek -- indeed demand -- assurances (privately, if not publicly) that India will refrain from field deployment of its nuclear weapons as a quid pro quo for any enhanced military cooperation.

Even more effective would be a coordinated message to New Delhi and Islamabad from the four major regional powers -- the U.S., Russia, China, and Japan -- that "business as usual" will cease if either field deploys its nuclear weapons; that such a dangerous, destabilizing action would result in an immediate halt in all four nations' economic and (where applicable) military support.

Unilateral sanctions after the fact have proven to be ineffective, but a carefully coordinated multilateral reminder of the costs involved in future destabilizing actions just might preclude both from taking the next step.

The time to act is now, while deployment plans are still on the drawing board in India and Pakistan and while the U.S., Japan and others are stepping up economic support to South Asia and the carrot of U.S. arms sales is still dangling in front of New Delhi.

What better way for the U.S., Russia, and China to demonstrate their commitment to a nuclear weapons-free world than by drawing a definitive line in the sand against field deployment and its potentially disastrous consequences on the Indian subcontinent.