After three months of deliberations, Obama will outline his plan in an address to the American public on Tuesday from the US military academy at West Point in New York.
Pentagon officials hope that Nato member states will supplement the US increase with up to 10,000 of their own troops and trainers - pushing the overall number of extra troops close to 40,000.
'Not open-ended'
Washington hopes the boost, which is expected to be phased in over the next 12 to 18 months, will create conditions that will eventually allow the number of US troops to be scaled back.
"You will hear the president discuss clearly that this [support for the war] is not open-ended," Robert Gibbs, a White House spokesman, said on Monday.
"This is about what has to be done in order to assume that the Afghans can assume the responsibility of securing their country," he said.
General Stanley McChrystal, the US and Nato commander in Afghanistan, told politicians that a troop reduction could begin by 2013, while the White House said it expected US forces out of the country by 2017 or 2018.
Rob Reynolds, Al Jazeera's correspondent in Washington, said Obama's announcement of the specific troop numbers would be less important than the US goals he sets out for the war.
"I think Obama is going to have to reintroduce the American people to exactly what these goals are - whether he is going to scale them up or down," he said.
Explaining the mission
In addition, he said, there is a contradiction in what the president is saying.
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| Obama has said the US commitment to Afghanistan will not be open-ended [AFP] |
"He is saying it is not an open-ended commitment and yet he is going to finish the job, which implies the troops will be there for as long as it takes.
"If the goal is to completely eradicate the Taliban, that would require more troops than I think any army has."
"The key is going to be for Obama to explain the mission – the mission is the important thing," he said.
"Putting troops in, in order to then pull out is something that will be difficult for people to understand."
Obama on Monday briefed Kevin Rudd, the Australian prime minister, in an Oval Office meeting and spoke with other leaders, including Gordon Brown, the British prime minister, the French and Russian presidents and the Italian prime minister.
"The president believes the situation in this region is a shared international challenge, so building on the work he's been doing in this regard," Gibbs said.
"The president will be in close consultation with our friends and allies throughout the day."
Obama's discussions with the leaders of Nato member countries came on the same day that Brown pledged to send 500 more British troops to Afghanistan.