Obama referred to a deteriorating military environment, but said, "Afghanistan is not lost."
The length of the presidential review drew mild rebukes from normally amiable NATO allies. There was sharper criticism from Republicans led by former Vice President Dick Cheney, who said the president was dithering rather than deciding.
Obama rebutted forcefully.
"Let me be clear: There has never been an option before me that called for troop deployments before 2010, so there has been no delay or denial of resources necessary for the conduct of the war," he told his audience of more than 4,000 cadets seated in Eisenhower Hall.
Most of the new forces will be combat troops. Military officials said the Army brigades were most likely to be sent from Fort Drum in New York and Fort Campbell in Kentucky; and Marines primarily from Camp Lejeune in North Carolina.
Officials said the additional 30,000 troops included about 5,000 dedicated trainers, underscoring the president's emphasis on preparing Afghans to take over their own security.
These aides said that by announcing a date for beginning a withdrawal, the president was not setting an end date for the war.
But that was a point on which McCain chose to engage the president at a pre-speech meeting with lawmakers before Obama departed for West Point. "The way that you win wars is to break the enemy's will, not to announce dates that you are leaving," McCain said later.
Obama's address represents the beginning of a sales job to restore support for the war effort among an American public grown increasingly pessimistic about success - and among some fellow Democrats in Congress wary of or even opposed to spending billions more dollars and putting tens of thousands more U.S. soldiers and Marines in harm's way.
Sen. Russ Feingold, D-Wis., and liberal House Democrats threatened to try to block funding for the troop increase.
Sen. Carl Levin, the Michigan Democrat who chairs a military oversight panel, said he didn't think Democrats would yank funding for the troops or try to force Obama's hand to pull them out faster. But Democrats will be looking for ways to pay for the additional troops, he said, including a tax increase on the wealthy although that hike is already being eyed to pay for health care costs. Another possibility is imposing a small gasoline tax that would be phased out if gas prices go up, he said.
The United States went to war in Afghanistan shortly after the Sept. 11, 2001, al-Qaida terrorist attacks on the United States.
Bin Laden and key members of the terrorist organization were headquartered in Afghanistan at the time, taking advantage of sanctuary afforded by the Taliban government that ran the mountainous and isolated country.
Taliban forces were quickly driven from power, while bin Laden and his top deputies were believed to have fled through towering mountains into neighboring Pakistan. While the al-Qaida leadership appears to be bottled up in Pakistan's largely ungoverned tribal regions, the U.S. military strategy of targeted missile attacks from unmanned drone aircraft has yet to flush bin Laden and his cohorts from hiding.