White House officials are aggressively promoting the idea of sending more U.S. troops to Iraq over the unanimous objections of the Joint Chiefs of Staff, according to news reports. This is the right idea at the wrong time – put forward for unclear reasons.

The White House has yet to answer the pointed questions of Colin Powell last weekend on CBS’s “Face the Nation”: “What mission is it these troops are supposed to accomplish? … Is it something that is really accomplishable? … Do we have enough troops to accomplish it?” Or, is this one last White House effort to look tough, whether or not it helps Iraq?

Iraq’s current chaos traces directly to Donald Rumsfeld’s deluded decision to send too few troops to Iraq to stabilize the country. Rumsfeld just departed with highest honors, as Dick Cheney proclaimed him “the finest secretary of defense” the nation has known. How ironic that the Bush team wants a troop surge at this very moment.

The number of U.S. troops is indeed an issue. The White House plan to turn security over to Iraqis is failing. Iraq’s government is weak, and its security forces are divided by sect and penetrated by sectarian militias. These security forces are often part of the problem, taking part in ethnic cleansing.

In theory, more U.S. troops could improve the situation, by helping to stabilize the Sunni areas of Baghdad and Anbar province. These areas remain the core of the security problem. They are often controlled by former senior Baathists and Sunni religious extremists, who have sought to provoke civil war by killing Shiite civilians. After three years of restraint, Shiite militias now seek revenge against Sunnis, deepening the civil strife.

Those Sunni moderates who don’t want to be ruled by extremists are too frightened to stand against them. Sunni tribal leaders and politicians who participate in the government are being assassinated, and now face the additional threat of Shiite militias.

Serious scholars who support a surge, like Fred Kagan of the American Enterprise Institute, argue that an increase in U.S. troops could bring security to Sunni and mixed areas of Baghdad, by clearing out the insurgents. U.S. troops could then stay on in partnership with Iraqis.

This “clear, hold and build” strategy could, again in theory, permit the return of normal life and services to Sunni areas. If insurgents were reined in, Sunni moderates would feel less fearful about joining the new system. And, crucially, if the number of Sunni attacks on Shiites dropped, the Shiite-led government could rein in Shiite militias, slowing down the civil strife.

“Clear, hold and build” worked in two of the few success stories in predominantly Sunni areas, the cities of Mosul and Tal Afar. The U.S. ground commanders in those cases understood – even though the Pentagon did not – that their first priority was to provide security and services for the local population.

Just this week, the Army and Marine Corps released a new counterinsurgency manual, the first in 20 years, that distills the principles for such operations. Would that the manual had been available years earlier.

But – here’s the key – when U.S. troops were cut by two-thirds in Mosul after one year, insurgents returned and the city dissolved into chaos. Tal Afar deteriorated for similar reasons.

“Clear, hold and build” is a long-term strategy, requiring a large number of troops to stay for years. Their numbers must be sufficient to blanket troubled areas and prevent insurgents from escaping to the next village.

Yet news reports say the White House is considering sending 15,000 to 30,000 more troops to Baghdad for six to eight months. That’s not enough time to “hold and build,” nor for the Iraqi government to get its act in order. So it’s unclear what would be the troops’ purpose, or what they could achieve.

Any boost in numbers would depend on retaining units now in Iraq for a longer time and accelerating the arrival of others. Powell said this weekend that such a surge “cannot be sustained.” Even if Congress were to expand the size of the Marines and Army, that increase would not come in time to enable an extended surge.

The Joint Chiefs oppose sending more troops because they feel the military has been broken by Rumsfeld. One Army officer sent me this e-mail, which reflects a much wider feeling in the military: “The idea of adding 20,000 is criminal. It’s not enough to do any good, but it’s more than enough to bring an already staggering Army to its knees.”

If the White House wants to increase troop levels, it must answer Powell’s questions: What indeed is their mission? What can be accomplished by a brief surge at this late date? And how does the president plan to man and fund the mission?

This would require President Bush to explain why insufficient troops were sent to begin with, and why he failed to supply the military with the resources it needed to do the job right. Without such frankness, a skeptical country won’t support him, nor would a surge make sense.