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Gen. Stanley McChrystal, the commander, said the number is the minimum needed to defeat al-Qaida and Taliban in Afghanistan, according to a copy of the secret reqeust disclosed by the Washington Post and other U.S. media outlets on Thursday.
The general presented three options for the president.
One is not to send any more troops to Afghanistan. The second is to send 40,000 troops as the minimum, and the third calls for a major increase in troops, far more than 40,000.
McChrystal recommends the second option, apparently acknowledging the fact that the much higher number will be impossible to get approved, given the U.S. military that is stretched so thin over the years of "war on terror."
Meanwhile, Obama and his aides are downplaying the troop numbers as the focus of the president's ongoing review of the Afghan strategy.
White House aides told reporters on Thursday that the focus of the strategy is now shifting away from the Taliban in Afghanistan to al-Qaida cells in Pakistan.
That shift, analysts said, could draw stark lines between the president and his generals.
The U.S. military linked al-Qaida and the Taliban as a dual enemy, and recommends a counterinsurgency strategy to defeat them, which would require more troops.
A final decision on the strategy adjustment, including troop levels, is still weeks away, according to the White House.