President Barack Obama speaks about the war in Afghanistan on Tuesday at the U.S. Military Academy at West Point, N.Y. Obama said he will send 30,000 additional U.S. troops to Afghanistan by next summer, and begin withdrawing them in July 2011.

After President Barack Obama delivered his speech Tuesday on his Afghanistan strategy, about 20 protesters peacefully demonstrated their opposition to the war outside the Douglas County Courthouse, 1100 Mass. Anne Burgess, right, expressed her view with her sign. Lawrence Coalition for Peace and Justice organized the event.

West Point, N.Y. ? Announcing a major expansion of the war in Afghanistan, President Barack Obama on Tuesday said the swift deployment of 30,000 troops would be enough to break the Taliban before the soldiers begin coming home in mid-2011 — a bet he is making because the U.S. cannot afford a drawn-out, costly campaign.

Describing Islamic extremism as “no idle danger, no hypothetical threat,” Obama outlined what would amount to a rapidly executed surge, rushing tens of thousands of combat forces into the country by next summer, while pledging that 18 months later they will begin to be brought back.

“I make this decision because I am convinced that our security is at stake in Afghanistan and Pakistan,” Obama said. “This is the epicenter of the violent extremism practiced by al-Qaida. It is from here that we were attacked on 9/11, and it is from here that new attacks are being plotted as I speak.”

The decision to send 30,000 additional soldiers had been widely anticipated. The more surprising element was Obama’s decision to set a specific month for the start of the soldiers’ return.

Based on Obama’s schedule, the war would begin to wind down nearly 10 years after it began. The timetable is likely to please members of Obama’s own party, who have pushed him to set a clear exit strategy for the war. But others expressed alarm that Obama had signaled an end to the surge even before it started.

“A date for withdrawal sends exactly the wrong message to both our friends and our enemies — in Afghanistan, Pakistan and the entire region — all of whom currently doubt whether America is committed to winning this war,” said Sen. John McCain, R-Ariz. “A withdrawal date only emboldens al-Qaida and the Taliban, while dispiriting our Afghan partners and making it less likely that they will risk their lives to take our side in this fight.”

But in a briefing with news columnists before his speech, Obama dismissed concerns that signaling a withdrawal date would encourage the enemy to wait for U.S. forces to leave.

“If you follow the logic of this argument then you would never leave,” Obama said. “Essentially, you’d be signing on to have Afghanistan as a protectorate of the United States indefinitely.”

Beyond that, Obama said that without a timetable the United States would have “very little leverage” to push the government of Afghan President Hamid Karzai to prepare for the day when it would have to handle security — and fend off the Taliban — on its own.