The new deployment over six months will bring America's troops in the country to more than 100,000, in the fight against Taliban fighters.
Obama also urged America's allies in Nato to send more troops.
Defending the war, he insisted “there were no parallels with Vietnam and that world security was at stake”.
Some 32,000 other foreign troops are serving in Afghanistan but Nato allies have been cautious about contributing further forces.
PHOTO CAPTION
US President Barack Obama speaks about the war in Afghanistan at the U.S. Military Academy at West Point, N.Y., Tuesday, Dec. 1, 2009
Agencies