Trends in Iraq seem to be moving in two different directions these days. The guerrilla war between the United States and insurgents continues, with mounting clashes and casualties. Yet the standoff with the Shiite leader Moqtada Sadr in Najaf and Kufa has ended, and those cities are no longer controlled by the Mahdi Army. The intractable security problems in Sunni areas, coupled with success in Shiite ones, might lead the Iraqi government (and Washington) toward a "Shiite strategy" in Iraq. But going down that path has its dangers. It would heighten Iraq's divisions along ethnic and religious lines. That could make today's problems look easy.

After the creation of the interim Iraqi government in June, many hoped that the insurgency would die down. It hasn't. Today it appears more organized, entrenched and aggressive than ever. The U.S. Army cannot use its military superiority to take Sunni cities from the guerrillas because that would produce heavy civilian casualties and fuel anti-Americanism. The interim Iraqi government itself may not have the necessary credibility to take on such a task. Prime Minister Ayad Allawi is a tough guy, but he is clearly aware of the limits of his legitimacy. And the Iraqi army will not be up to the job for at least another year. In these circumstances, it's difficult to see how the insurgency will diminish in strength. Last week Iraq's ambassador to the United Nations, Sameer Shaker Sumaidaie, predicted to the Scotsman newspaper that unless the United States and Britain added "a considerable amount" of troops to Iraq, the insurgency could grow.

But for all its resilience, the insurgency has not spread across the country, nor is it likely to. Its appeal has clear limits. While it has drawn some support from all Iraqis because of its anti-American character, the insurgency is essentially a Sunni movement, fueled by the anger of Iraq's once-dominant community, which now fears the future. It is not supported by the Shiites or the Kurds. (The Shiite radical Sadr has been careful not to align himself too closely with the insurgency, for fear of losing support among the Shiites.) This is what still makes me believe that Iraq is not Vietnam. There, the Viet Cong and their northern sponsors both appealed to a broad nationalism that much of the country shared.

Hence the temptations of a "Shiite strategy." Such an approach would view the Sunni areas in Iraq as hopeless until an Iraqi army could go in and establish control. It would ensure that the Shiite community, as well as the Kurds, remained supportive of Allawi's government and of the upcoming elections. It would attempt to hold elections everywhere -- but if they could not be held in the Sunni areas, elections would go forward anyway. That would isolate the Sunni problem and leave it to be dealt with when forces become available.

The Shiites are easier to handle. They supported the U.S. invasion, which rid them of Saddam Hussein's tyranny. They have also disciplined their own, curbing Sadr's violent challenges to the government. Allawi and Washington handled this well, careful not to blast their way through Najaf's Imam Ali shrine (a "sensitive" war, one might say). But the key was that Ayatollah Ali Sistani, the towering Shiite figure, does not want Sadr to disrupt the path to elections (and thus Shiite majority rule).

A Shiite strategy is understandable but risky. If the Sunnis end up with no representatives, they will have even less incentive to support the new Iraqi order. Today a significant number of Sunnis feel disenfranchised, and thus they support the guerrillas (estimates vary from 25 percent to 65 percent). If they are cut out of the government, all will feel disenfranchised. And to have one-fifth of the population -- people who are well trained and connected -- supporting an insurgency will make it extremely difficult to defeat militarily.

Allawi is trying hard to co-opt Sunni tribal and religious leaders. But the structure of Sunni political authority is fractured; there is no dominant Sunni leader like Ayatollah Sistani. And Allawi's plans to offer insurgents amnesty were derailed by the U.S. objection to pardoning anyone who was involved in killing Americans.

In Iraq the one truly pleasant surprise so far is that there has been little religious and ethnic bloodshed. Many of the experts who counseled against an invasion predicted that after Hussein's fall, the Sunnis, Shiites and Kurds would tear each other apart. Nothing like this has happened. The problems -- of resistance, nationalism and anti-Americanism -- have been quite different. But the balance is fragile. If the United States and the Iraqi government played a sectarian strategy, things could unravel.

In many of their colonies the British would often favor a single group as a quick means of gaining stability. Almost always the results were ruinous: a trail of civil war and bloodshed. If Allawi and the United States make the same mistake, there will be 140,000 American troops in the middle of it all.