Can one back President Bush's new strategy in Iraq? Yes. For all its serious faults, his new approach is the first one since the fall of Baghdad to offer a chance to reverse the radicalization of Iraq. But it needs revision quickly.

Too much of this new plan leaves unchanged the disastrous approach of John Abizaid and George Casey, the two top generals on Iraq. The new offensive, assuming it doesn't peter out through a slow arrival of soldiers, or become enfeebled by "Iraqi leadership" in its execution, envisions a too-small U.S. force doing too much. Recent remarks by Defense Secretary Robert Gates -- predicting troop reductions within a year, and saying that we might not need an additional five brigades in Baghdad for a successful operation -- are a frightening echo of the self-defeating, undermanned optimism that came from the U.S. military under Mr. Gates's predecessor.

* * *

The good news is that by emphasizing a military, not political, strategy to diminish Iraq's debilitating violence, the president has correctly set aside one of the primary factors destroying the Shiite Arab center. While waiting for a "political solution" to the Sunni insurgency, we watched Shiite timidity and patience turn to anger -- and to a revenge which now threatens the integrity of the Shiite-led Iraqi government. Gens. Abizaid and Casey had gambled that they could stand up an effective Iraqi military and police against the Sunnis before violence threatened everything in Baghdad. That bet collapsed with the destruction of the Shiite shrine in Samarra in February 2006 -- but the administration kept playing the same hand as if nothing had happened. The reversal of this soft-power, politics-not- troops mentality is an essential step forward.

Still, David Petraeus, who will succeed Gen. Casey as the overall boss in Iraq and who is one of America's finest, most adaptable commanders, may have to perform a miracle to compensate for this shortfall in manpower, especially if the required five brigades for Baghdad take months to arrive, and if Washington allows the offensive to move forward before he is even in charge. The president can pre-empt these lethal problems by ensuring Gen. Petraeus's rapid arrival in Iraq and by allowing him to determine how many soldiers he needs.

Nevertheless, there is a dismaying hesitancy in the military's and the White House's deliberations on this conflict. Although the president wants a new approach, the Pentagon, the State Department and even the National Security Council appear wedded to the past. The contradiction between what the president says and what his government does has never been greater. We need to move rapidly: The enemy is digging in and the drift to full-scale civil war is gaining speed.

The administration needs to rethink its understanding of Iraqi culture and politics, as the "new" strategy still contains ideas that have catastrophically guided American officials in the Green Zone ever since Sunni Arab insurgents started killing Americans in significant numbers. U.S. officials still believe they must soon see sectarian reconciliation, a reversal of de-Baathification, and a nonsectarian, equitable distribution of oil wealth.

All these achievements are meant to placate the aggrieved Sunni Arabs, who represent 15% of the population. But no one knows how many Sunni Arabs sympathize with their brethren who've been killing Shia. It certainly seemed like a very large number before the Shiites started counterattacking through their militias. The statements of Iraqi Sunni Arab organizations, the coverage of the Iraqi Sunni press and the region's Sunni Arab media, which often quotes and echoes the opinions of Iraqi Sunnis, suggest strongly that there is substantial communitarian support for both domestic and foreign suicide bombers.

For the serious ex-Baathists, Sunni supremacists and Iraqi Sunni fundamentalists -- the lethal hardcore of the insurgency -- it's still a good bet that they're not into democratic negotiations. They probably don't think much at all about an equitable distribution of oil revenues -- or wanting their jobs back in the new army's officer corps.

De-Baathification for the Shiites and the Sunnis is really about only one thing: the army. But from the moment the U.S. started building a more representative Iraqi military in 2003, there was no way in hell the old Baathist Sunni officer corps could come back. And now, with the Shiites killing Sunnis, even the most enlightened of the proscribed Baathist officers (this isn't a large group) know that return would be suicide. No one knows how many Sunni Arabs would turn against their uncompromising, murderous brethren and align themselves with Shiites if the right "deal" were struck. It's a very good guess that such men, if they exist in any number, would get mowed down by their radical compatriots.

If the U.S. and Iraqi governments are going to bring peace to the "Sunni triangle," they must break the back of the insurgency. A minority, used to the prerogatives of a communitarian dictatorship, the Sunnis have been trying to derail the new Iraq: They must come to know that they will lose everything if they don't abandon violence as their principal political tool. They must know that if they choose to cease their violent opposition, they will not be murdered for doing so. This means, as it has always meant, a combined American and Shiite Iraqi occupation of major Sunni Arab cities. If the Sunni community hasn't hopelessly gone into a dominance-or- death opposition, then it could still come to its senses, provided the violent hardcore among them is neutralized and the Shiites and the Kurds allow them sufficient access to oil wealth. Shiite death squads have certainly taught the Sunnis of Baghdad that there are worse things than infidel U.S. troops in their neighborhoods.

Baghdad is the first step. And as retired general Jack Keane and the military historian Frederick Kagan have been pointing out, restoring security in Baghdad will take at least 18 months and all the troops the president pledged. To quote Gen. Keane: "We need all five brigades in Baghdad as soon as possible. It will take three to four months to clear neighborhoods of death squads and insurgents, and at least the rest of the year to establish proper security for the population." This is going to be a long, hard slog. And the Americans, not the Iraqis, are going to have to lead it.

The president's stated contention -- that Prime Minister Nouri al-Maliki's army and police will lead efforts to cleanse the city, while the Americans just support them -- will produce dismal results. Mr. Maliki's pride doesn't win battles. George Bush has been fond of underscoring the counterinsurgency success in Tal Afar, in which the Iraqi army played an important supporting role. If Gen. Petraeus is really put into a supporting role in the Battle of Baghdad, then we've lost already.

Gen. Petraeus will have to deal with Muqtada al-Sadr. The thuggish son of Iraq's most revered clerical family, he has become for many Shiites in Baghdad a rapturously praised defender. This esteem is merited: He, not any American general, increased the security of the average Shiite in the capital. And if he is smart, he'll attack the Americans before they have the chance to deploy much new strength. If the Americans successfully down Sunni insurgents in the capital, then they will go after Mr. Sadr.

But the U.S. military should absolutely not go after Mr. Sadr first. We may barely have sufficient forces to handle a one-front war against Sunni insurgents and holy warriors. We need to show the Shiite community, which by no means has embraced Mr. Sadr's radicalism en masse, that the Battle of Baghdad's primary thrust isn't against the capital's large Shiite ghetto.

The key here is how Shiites view the first encounter. If it goes against the insurgents, then a subsequent attack on Mr. Sadr and his militia might not provoke a large-scale uprising. And he just may play along. He and his forces were mauled by the Americans in 2004. Since then they haven't been particularly bold in attacking U.S. soldiers. Mr. Sadr has recently manifested some statesmen-like behavior, and has been more correct in his behavior toward Grand Ayatollah Ali Sistani, the spiritual guide of Iraq's Shia and a bulwark of moderation. Yet Washington ought to plan on Mr. Sadr hitting U.S. forces -- another reason why Gen. Petraeus, who appears acutely sensitive to the Sadr conundrum, should be given as many brigades as the U.S. can rapidly pull together.

Wars are often decided by one battle, where the genius and resources of one commander proves decisive. We are undoubtedly at that point in Iraq. The Bush administration should ensure that Gen. Petraeus has everything he needs, and that any opposition inside the military to him and a larger, longer counterinsurgency campaign is squelched. America and Iraq probably won't get a second chance.

Mr. Gerecht is a resident fellow at the American Enterprise Institute.