Two years ago, my wife and I vacationed in Pakistan's Swat Valley. We spent an afternoon sightseeing in the hills, visiting stupas in the dense pine forests and carvings of the Buddha etched into sheer granite cliffs, remnants of the Buddhist civilization that had thrived in the valley for centuries. Later, we played badminton back at our hotel.

In those days, guest rooms were full, and policemen patrolled the streets. When I asked the hotel's night manager about Maulana Fazlullah, the Taliban commander whose headquarters were just a few miles away, he put a finger to his lips and shook his head, reflecting the national response to the Swat Taliban: Ignore them, and they'll go away.

That policy, lambasted by many as appeasement, actually made sense in the context of Swat's relatively peaceable history and culture. But not long after our visit, Fazlullah's cohorts began defacing the valley's rich legacy -- and all the policy assumptions that went with it -- when they blasted some of the Buddha statues, mimicking the Taliban's destruction of the giant Buddhas in Bamiyan, Afghanistan. In October 2007, I went back to Swat to interview Fazlullah. This time, the hotel was vacant and the Taliban were conducting public lashings. In just months, Fazlullah had transformed Swat from an idyllic travel destination into a militant sanctuary. Still, the Pakistani government clung to the hope that he would just go away.

Then Fazlullah went a step too far. In April, a detachment of his fighters advanced out of Swat into the neighboring district of Buner, bringing them closer than ever to the capital, Islamabad. That finally got the attention of the Pakistani army, which has been pounding the Taliban ever since. According to army spokesmen, the military has forced a Taliban retreat from Buner while reclaiming Swat's main city of Mingora and reestablishing government control throughout the valley.

Now hopes are high in many quarters that the Pakistani military will ride this momentum into the more crucial battle -- in South Waziristan, the home base of Baitullah Mehsud, Pakistan's terrorist honcho, and untold numbers of al-Qaeda fighters. Last week, the United States delivered four MI-17 cargo helicopters to Pakistan to support the army's fight against the Taliban. Pakistani President Asif Ali Zardari has called the Swat operation "just the start" and has declared, with cheering from the Western sidelines, "We're going to go into Waziristan."

But this enthusiasm should be tempered. The Obama administration has shown a refreshing realism in its policy toward Afghanistan and Pakistan, and if it wants to succeed there, it should encourage the Pakistani army to stay out of Waziristan -- at least for now.

South Waziristan is an area slightly smaller than Connecticut. Yet after a couple of thousand years of fighting -- and defeating -- anyone who has dared tread too close, Waziristanis have acquired an outsize reputation as recalcitrant tough guys. "No patchwork scheme," Lord Curzon, the turn-of-the-20th-century British viceroy of India, declared, "will settle the Waziristan problem. Not until the military steamroller has passed over the country from end to end, will there be peace. But I do not want to be the person to start that machine." His recent bluster notwithstanding, Zardari doesn't want to start it either.

Unlike Swat, South Waziristan has been under Taliban rule for most of the past decade. In March 2004, Pakistani troops entered this southernmost tribal agency in their first bid to crush the militants. A month later, the Taliban were clobbering the army, and former president Pervez Musharraf was scrambling to find an exit strategy. Since then, the Taliban have repelled several other operations and, in 2007, kidnapped more than 200 soldiers.

Does that make it impossible for the Pakistani army to defeat them today? Not necessarily. But it is unrealistic to believe that the Pakistani army could continue fighting Taliban remnants in Swat, remain heavily deployed along the border with India (where they'll remain until, well, forever) and dedicate enough troops in South Waziristan to resemble a steamroller.

Another stumbling block is the Pakistani military's roster of assets in South Waziristan: They have an almost equal number of jihadist friends and enemies. In the Waziri areas (the region is populated by two tribes, Wazirs and Mehsuds), some Pakistanis see a Taliban leader named Maulvi Nazir as a strategic asset, the kind of "good" Talib who is only interested in fighting the Americans in Afghanistan. Nazir endeared himself to the officer corps when he expelled hundreds of Uzbek militants from the Waziri areas in March 2007.

If the Pakistani government considers Nazir a good Talib, then Baitullah Mehsud is definitely a bad one. How bad? The U.S. government is offering $5 million for his head, compared with the $600,000 bounty Islamabad put up for Fazlullah. Whether Mehsud is eight times more dangerous than Fazlullah remains to be seen, but he is undoubtedly more capable of committing catastrophic acts of terrorism. Pakistani and U.S. intelligence agencies believe he masterminded the assassination of Benazir Bhutto and has a pool of trained suicide bombers waiting for orders.

Nazir is no saint, though. There have been several drone attacks, including one that killed al-Qaeda's leading WMD expert, in his territory. But the Pakistani army won't come for him, and he knows it. He has sounded unfazed by rumors of an impending invasion. He has even reportedly told Mehsud that though he can't join him in fighting Pakistani forces, he'll guarantee him safe passage through Waziri areas to Afghanistan to fight NATO forces there.

And finally, there's al-Qaeda. In his Cairo speech, Obama declared that the United States doesn't want to stay in Afghanistan forever. But neither he nor any future president will be able to ponder withdrawal without having either killed or captured Osama bin Laden and his deputy, Ayman al-Zawahiri. Both men are suspected of having bunked down in South Waziristan at various points. If uber-stealthy drones and commandos haven't found them so far, a noisy, invading battalion of Pakistani troops probably won't, either.

In some ways, Swat and South Waziristan today are like Afghanistan and Iraq in 2003: Rushing into the latter would almost certainly jeopardize success in the former. Pakistan's battle against the Taliban won't be won or lost in the hills, but in the hearts of ordinary Pakistanis, and especially the Pashtuns who live on either side of the Afghanistan-Pakistan border. They are watching more closely than anyone to see whether the army is serious about finishing off Fazlullah's Taliban. They are also watching more closely than anyone to see the fate of millions of Pashtuns who have fled their homes in and around Swat as a result of the army offensive.

The United Nations estimates that these refugees are the largest community of internally displaced people in the world. Some are housed in official refugee camps, but most are living in impromptu ones that, like all such camps, are crowded, filthy and short on food. And yet these camps provide an opportunity for the Pakistani government (with significant financial backing from the United States, which recently promised $300 million) to allay the refugees' hardships and regain the confidence of Swat's population, as well as of other Pashtuns who've watched the Taliban take over their areas while the government stood aside.

Eventually the refugees will return home, and the Taliban will emerge from their hideouts. When that happens, if the residents of Swat believe that the authorities won't stand aside, the government will have achieved a more critical goal than any military success so far. Daily battles between the army and the Taliban are far less important in the grand scheme than the refugees' plight. A war in South Waziristan would compound the refugee crisis.

I'm not suggesting that the White House encourage the Pakistani military to abdicate to the militants, to return to its ambivalent approach of years past. But as rumors of an imminent operation in South Waziristan grow, the Obama administration and the Pentagon should realize that the significant change in will on the part of the Pakistani army might not make up for shortfalls in capacity. South Waziristan is far more complex, difficult and challenging terrain than Swat. A battle there would be no leisurely game of badminton.