"It's not going to happen this week," Robert Gibbs, the White House spokesman, said.
"Obviously the first possible time would be some time next week."
Range of options
Gibbs said that Monday's meeting of the national security council was a chance to "go through some of the questions that the president has".
The US currently has nearly 68,000 troops deployed to fight a resurgent Taliban and al-Qaeda in Afghanistan. As Obama debates a revised strategy in the eight-year war, officials say he is considering four options.
One option is the request put forward by the top US commander in Afghanistan, General Stanley McChrystal, for 40,000 more troops to secure the towns and cities.
Another option, said to be carrying the most favour among officials, is an increase of 30,000. Washington could then try to convince Nato allies to contribute, bringing the number of troops to the 40,000 McChrystal recommended.
Options three and four include significantly lower troop deployments, from 20,000 to 15,000, most of who would serve as trainers for the Afghan security forces.
Obama and his advisers have debated options ranging from sending the tens of thousands more troops requested by McChrystal to limiting troop increases and concentrating on attacking al-Qaeda targets.
But reports have suggested that the advisers are rallying around options that would see a deployment of between 30,000 and 40,000 troops and trainers sent to Afghanistan.
Moves to send more troops face opposition from a public disillusioned with the long-running conflict and politicians from Obama's own Democrat party who say the US must start looking for a way out of Afghanistan.
A Washington Post
-ABC News poll found last week that 46 per cent of Americans support a large influx of troops to battle Taliban fighters and train the Afghan military, while 45 per cent favour a smaller number of military personnel to focus on training Afghan security forces.
Obama's decision has also been complicated by concerns about corruption and governance in the administration of Hamid Karzai, the Afghan president.
Karzai was sworn in for a second term last week after an election marred by widespread fraud and farce as his main challenger refused to take part in a second round run-off.Delays and doubts
The delays have prompted criticism from opposition Republicans, who tend to favour sending large numbers of troops.
Dick Cheney, the former vice-president, told a radio show on Monday: "The delay is not cost-free.
"Every day that goes by raises doubts in the minds of our friends in the region about what you're going to do, raises doubts in the minds of the troops."
Gibbs defended the president, saying that Obama was making "a complicated decision".
"I think the American people want the president to take the time to get this decision right, rather than to make a hasty decision," he said.
Meanwhile, seven troops, including four from the US, were killed in attacks across Afghanistan.
Two US soldiers were killed by a roadside bomb, another died in an attack and a fourth was killed by an improvised explosive device, the NATO-led International Security Assistance (Isaf) force said.
The other three soldiers killed were Afghans hit by a bomb blast while on patrol in southern Helmand province.
The Isaf force currently has about 71,000 troops in Afghanistan, nearly half of them American. The US military also has another 36,000 soldiers in Afghanistan who serve outside Nato under independent command.