President Obama's decision on how to proceed in Afghanistan is one of the most important he's likely to face in office. Unfortunately it appears that he will risk the success of his administration's new strategy for Afghanistan by providing less troop reinforcements than his military commanders have recommended.

The Obama administration deserved praise earlier this year for recognizing that Afghanistan needed more high-level attention, resources and U.S. troops. In March the president announced the adoption of a new counterinsurgency strategy to protect Afghan civilians, build up the Afghan army and police, provide more foreign aid and help Afghans build a more effective national government. He also dispatched 21,000 more U.S. troops to lay the foundation of the new strategy and selected Gen. Stanley McChrystal to lead the effort.

In late August McChrystal submitted a situation report that concluded that more U.S. troops were required to carry out the strategy. McChrystal reportedly requested about 40,000 more troops. But the White House apparently has gotten cold feet about implementing its own strategy, announced with much fanfare last March, opting for a commitment to provide 30,000 more troops for a period of three years.

This downsizing of urgently requested troop reinforcements could lead to a dangerous and tragic outcome. If Obama retreats to a "McChrystal Light" option that shortchanges his own hand-picked commander, it will greatly increase the risk of failure, not only in Afghanistan but in the struggle against Islamist radicals in neighboring Pakistan. It could result in a downward spiral of security in Afghanistan: a resurgent Taliban, eventual collapse of the Afghan government, an even bloodier civil war, renewed humanitarian crisis and a refugee exodus. Moreover, the Taliban will bring back not just their ally al-Qaida, but a rogues' gallery of almost every major Islamist insurgent movement in the world today.

Resorting to half-measures would be courting disaster. Like it or not, Obama is a wartime president who must make timely decisions on difficult issues, sometimes with no guarantee of success. The United States needs a decisive commander in chief, not a professorial hair-splitter trying to transcend the differences of opinion of his staff.

The basic concept of the McChrystal strategy is sound. U.S. troops must increase the focus on protecting Afghan civilians to reduce the space in which the Taliban can operate freely. A major part of this effort must be a "civilian surge" to help build the capacity of the Afghans to govern, fight corruption, restore the rule of law and revitalize the Afghan economy. But security must come first. There must be additional American "boots on the ground" to defend civilians -- and the sooner, the better.

To shore up waning popular support for the war, the president needs to be clear with the American people about what is at stake in Afghanistan and why the war is not only necessary but winnable. And he should stress that although the war in Afghanistan is costly in terms of casualties and defense spending, losing that war would be much more costly and dangerous for the future security of the U.S.

Obama also needs to lay the groundwork for a bipartisan approach to Afghanistan that would attract renewed popular support. He should emphasize that this is not "Bush's war" or "Obama's war" but America's war. And he should promise to give his military commanders the tools that they need to fight and win that war. That would be change that most Americans can believe in.

James Phillips is Senior Research Fellow for Middle Eastern Affairs in the Douglas and Sarah Allison Center for Foreign Policy Studies, a division of the Kathryn and Shelby Cullom Davis Institute for International Studies, at The Heritage Foundation.