WASHINGTON - President Barack Obama will announce the critical next steps in America's decade-long war in Afghanistan on Wednesday, outlining both a plan to start bringing thousands of US troops home next month and a broader withdrawal blueprint aimed at giving Afghans control of their own security in 2014.

But even as Obama finalizes those plans, there are deep divisions in his administration, with military leaders favoring only a gradual reduction in troops but other advisers advocating a significant decrease in the coming months.

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Administration officials say Obama is still working through the details on how many troops will start leaving Afghanistan in July, his self-imposed deadline for beginning the drawdown. He is considering a range of options presented to him last week by Gen. David Petraeus, the top US and NATO commander in Afghanistan.

"He's finalizing his decision. He's reviewing his options," White House spokesman Jay Carney said Monday.

Obama is expected to make Wednesday's announcement in Washington. On Thursday, he will visit troops at Fort Drum, the upstate New York military base that is home to the 10th Mountain Division, one of the most frequently deployed divisions to Afghanistan and Iraq.

While much of the attention is focused on how many troops will leave Afghanistan next month, the more telling aspects of Obama's decision center on what happens after July, particularly how long the president plans to keep the 30,000 surge forces he sent in 2009 in the country.

There is a growing belief that the president must at least map out the initial withdrawal of the surge troops when he addresses the public. But whether those forces should come out over the next eight to 12 months or slowly trickle out over a longer time is hotly debated.

Military commanders want to keep as many of those forces in Afghanistan for as long as possible, arguing that too fast a withdrawal could undermine the fragile security gains in the fight against the Taliban insurgency in Afghanistan, the al-Qaida training ground for the Sept. 11 attacks. There are also concerns about pulling out a substantial number of US forces as the heightened summer fighting season gets under way.

Retiring Defense Secretary Robert Gates has said he believes the initial drawdown should be "modest".

But other advisers are backing a more significant withdrawal that starts in July and proceeds steadily through the following months. That camp believes the slow, yet steady, security gains in Afghanistan, combined with the death of Osama bin Laden and US success in dismantling much of the al-Qaida network in the country give the president an opportunity to make larger reductions this year.

There is also growing political pressure on Capitol Hill for a more significant withdrawal. Twenty-seven senators, Democrats as well as Republicans, sent Obama a letter last week pressing for a shift in Afghanistan strategy and major troop cuts.

"Given our successes, it is the right moment to initiate a sizable and sustained reduction in forces, with the goal of steadily redeploying all regular combat troops," the senators wrote. "The costs of prolonging the war far outweigh the benefits."

There is broad public support for starting to withdraw US troops. According to an Associated Press-GfK poll last month, 80 percent of Americans say they approve of Obama's decision to begin withdrawal of combat troops in July and end US combat operations in Afghanistan by 2014. Just 15 percent disapprove.

Obama has tripled the number of US forces in Afghanistan since taking office, bringing the total there to about 100,000. The 30,000 troop surge he announced at the end of 2009 came with the condition that he would start bringing forces home in July 2011.

The president took months to settle on the surge strategy. This time around, aides say the process is far less formal and Obama is far more knowledgeable about the situation in Afghanistan than he was in 2009, his first year in office.

Obama has said the July withdrawal will be "significant," though aides haven't quantified that. They do say Obama sees the initial drawdown in July as part of a larger strategy aimed at ending the US combat mission in Afghanistan by the end of 2014 and turning security responsibility over to the Afghans.

On a trip to Afghanistan earlier this month, Gates advocated for a comprehensive decision from the president.

"I think to make a decision on July in complete isolation from anything else has no strategic meaning," Gates said. "And so part of that has to be kind of, what's the book end? Where are we headed? What's the ramp look like?"

There are also indications that the administration, having learned from the US experience in Iraq, will set deadline dates for the drawdown as it progresses, in order to keep pressure on the Afghans and give Congress mileposts.

With Iraq as a blueprint, commanders will need time to figure out what they call "battlefield geometry" - what types of troops are needed where. Those could include trainers, intelligence officers, special operations forces, various support units - from medical and construction to air transport - as well as combat troops.

Much of that will depend on where the Afghan security forces are able to take the lead, as well as the state of the insurgency. Part of the debate will also require commanders to determine the appropriate ratio of trainers versus combat troops.