FACTBOX: How Obama's Afghan strategy is shaping up

(Reuters) - The centerpiece of President Barack Obama's revised war strategy in Afghanistan is expected to be the deployment of about 30,000 more U.S. troops to secure population centers, step up the fight against the Taliban and train Afghan security forces to gradually assume control.

The strategy will blend a broad-based counterinsurgency with hunt-and-kill counterterrorism tactics.

Washington hopes the buildup, expected to be phased in during the next 12 to 18 months, will create conditions to allow an eventual U.S. troop drawdown and handover to Afghan forces over a three- to five-year period, officials said.

Obama is not expected to announce a specific pullout date when he outlines his strategy in an address to the American people on Tuesday night from the U.S. Military Academy at West Point, New York, officials said.

STRATEGY TO MIX COUNTERINSURGENCY, COUNTERTERORRISM

Obama will continue the existing counterinsurgency strategy with a greater focus on protecting major Afghan population centers along with agricultural areas and transportation routes, officials said.

This will be combined with a counterterrorism campaign, advocated by Vice President Joe Biden, using unmanned aerial drones and special operations forces to combat Taliban and al Qaeda fighters along the Afghanistan-Pakistan border and possibly in Afghanistan's more sparsely populated areas.

TOP PRIORITY WILL BE TRAINING AFGHAN FORCES

The White House said a top priority for Obama will be accelerating the training of Afghan security forces to take over responsibility from U.S. and NATO troops.

One leading proposal would set the goal of having about 400,000 Afghan army troops and national police officers, more than twice the forces' current size, by 2012, a year earlier than currently planned.

But several key administration officials doubt that accelerated timetable and 400,000-man goal can be achieved.

OBAMA TO STRESS ROUGH HANDOVER, DRAWDOWN TIMEFRAME

U.S. officials said a transition to greater Afghan control could begin quickly in parts of Afghanistan that are more stable. Britain has called for the transfer of at least five Afghan provinces to "lead Afghan control" by the end of 2010 but it is unclear what that would entail.

General Stanley McChrystal, the top U.S. and NATO commander in Afghanistan, has told lawmakers that a troop drawdown could begin by 2013.

But officials said Obama was unlikely to be that specific and envisaged a more gradual, 3-5 year transition period for handing over greater authority to the Afghans and drawing down Western forces from their post-surge peak.

The White House says it sees U.S. forces out of the country by 2017-2018.

Defense Secretary Robert Gates said the U.S. withdrawal plan in Iraq was a possible model, whereby troops pull back and eventually out of city centers as Afghan forces assume the leading role.

TROOP INCREASE

Officials said Obama was poised to authorize sending approximately 30,000 more troops to Afghanistan, the option favored by several of his top national security and military advisers, including Gates.

Pentagon officials hope NATO member-states eventually will supplement the buildup with up to 10,000 of their own troops and trainers, pushing the overall number closer to the 40,000 recommended by McChrystal to counter a resurgent Taliban.

Britain has said it expects countries to pledge a further 5,000 troops on top of those sent by the United States.

Currently, there are roughly 68,000 U.S. troops and 42,000 allied forces in Afghanistan.

Leading the buildup will likely be an 8,000-plus Marine Expeditionary Brigade, followed by at least three Army brigades, typically made up of about 4,000 soldiers each.

Commanders want the Marines concentrated in Taliban strongholds in southern Afghanistan, including Kandahar and Helmand, the group's opium-producing heartland.

U.S. reinforcements also are expected to be sent to eastern Afghanistan near the border with Pakistan.

In addition to the 30,000-plus troop option, Obama considered a 20,000-plus deployment that might be more politically palatable for his Democratic allies in Congress. That number would allow McChrystal to accelerate the training of the Afghan army and police but would provide him with few additional resources for a broader counterinsurgency.

The smallest increase on the table called for an additional 10,000 to 15,000 troops to focus on training Afghan forces.

STAGED DEPLOYMENT

The Pentagon envisages carrying out the anticipated troop buildup in Afghanistan gradually, giving Obama the option of changing course before all of the new troops are in place if the strategy does not have the desired affect or if the Afghan government fails to meet its commitments.

Military officials said Afghanistan's poor infrastructure would make it difficult to field and equip more than a single brigade every quarter.

The first large-scale brigade under the expected buildup, accompanied by support units, could arrive before spring, when fighting typically picks up. Due to logistical hurdles, the buildup may not be complete until mid-2011.

ANTI-CORRUPTION 'COMPACT' WITH AFGHAN GOVERNMENT

A key part of Obama's strategy will be benchmarks for President Hamid Karzai's government to crack down on corruption and improve governance. U.S. officials say getting Karzai to do so is critical to a successful counterinsurgency that hinges on Afghans supporting their government instead of the Taliban.

Gates sees no quick fix to those problems and top officials said the United States could withhold aid contracts to pressure Karzai's government to act.

DIVIDE AND CONQUER

Administration officials say Obama wants greater outreach to groups that fight alongside the Taliban but could be persuaded to lay down their weapons in exchange for a greater role in local governance and Western-funded development.

As part of the revised strategy, the United States wants to see a crackdown on Taliban insurgent leaders based in Pakistan, including Mullah Omar and an allied network headed by veteran commander Jalaluddin Haqqani. Islamabad has been reluctant to act against them, U.S. officials say, citing suspected links between the militants and elements of Pakistani intelligence.

PAYING THE BILLS

The White House Office of Management and Budget estimates it will cost about $1 million a year for each additional soldier sent to Afghanistan. That means a 30,000- to 40,000- troop increase would add about $30 billion to $40 billion a year to the war's already soaring cost.

War spending in Afghanistan has more than doubled in the past year, reaching $6.7 billion in June alone. Pentagon officials worry that sticker shock could fuel congressional opposition to Obama's expected buildup.

(Reporting by Adam Entous in Washington; Editing by David Storey)