The Voice of America said the Pentagon described the deployment as a "one time, extraordinary" event with Bush acting on a recommendation from Defense Secretary Robert Gates. Senior military commanders had submitted the request for additional Marines last Friday.
Pentagon Press Secretary Geoff Morrell said the deployment in March and April will "greatly enhance" NATO's ability to deal with any spring offensive by the Taliban, VOA reported.
Of the additional 3,200 troops, 2,200 were expected to join the 40,000 NATO-led forces. The reinforcements would bring the number of U.S. troops in Afghanistan to its highest number since the fall of 2001, The Daily Telegraph reported.
About half of the 26,000 U.S. troops currently in Afghanistan are part of the NATO-led International Security Assistance Force. Some of the additional troops would train Afghan security forces.
Afghanistan has seen a sharp increase in Taliban violence in the past two years, with the southern and eastern regions of the country bearing the brunt of the insurgency.