Washington (CNN) -- President Barack Obama announced Wednesday night that all of the 33,000 additional U.S. forces he ordered to Afghanistan in December 2009 would be home within the next 15 months.

In a nationally televised address from the East Room of the White House, Obama said 10,000 of the so-called "surge" forces would withdraw by the end of this year, and the other 23,000 would leave Afghanistan by September 2012.

Calling the surge "one of the most difficult decisions that I've made as president," Obama said the military campaign was "meeting our goals" in Afghanistan and the draw-down would begin "from a position of strength."

U.S. troop levels

"Al Qaeda is under more pressure than at any time since 9/11," Obama said. "Together with the Pakistanis, we have taken out more than half of al Qaeda's leadership. And thanks to our intelligence professionals and Special Forces, we killed Osama bin Laden, the only leader that al Qaeda had ever known. This was a victory for all who have served since 9/11."

At the same time, Obama said the Afghanistan drawdown and the simultaneous winding down of the war in Iraq would allow the United States to begin refocusing attention and resources on efforts to resolve economic and other problems and being trying to unify a politically divided nation.

 

"America, it is time to focus on nation building here at home," the president said.

The troop withdrawals from Afghanistan will begin next month, as promised when Obama ordered the surge in a speech 18 months ago at the U.S. Military Academy at West Point, New York.

After the departure of all the surge forces, the total U.S. military deployment in Afghanistan would be just under 70,000 troops.

Obama's time frame would give U.S. commanders another two "fighting" seasons with the bulk of U.S. forces still available for combat operations.

It also would bring the surge troops home before the November 2012 election in which Obama will seek a second term.

Trepidation about what's next

Initial reaction was varied, with outgoing Defense Secretary Robert Gates supporting Obama's decision while congressional leaders were divided between those who wanted a faster withdrawal and others calling for caution in leaving Afghanistan.

"It's important that we retain the flexibility necessary to reconsider troop levels and respond to changes in the security environment should circumstances on the ground warrant," said House Speaker John Boehner, R-Ohio, in a statement. "It is my hope that the president will continue to listen to our commanders on the ground as we move forward. Congress will hold the Administration accountable for ensuring that the pace and scope of the drawdown does not undermine the progress we've made thus far."

Democratic colleagues of Obama expressed support for starting the withdrawal but said it should be more troops leaving faster than the president announced.

"It has been the hope of many in Congress and across the country that the full drawdown of U.S. forces would happen sooner than the president laid out -- and we will continue to press for a better outcome," House Minority Leader Nancy Pelosi, D-California, said in a statement.

According to senior administration officials, the troop surge fulfilled a strategy to refocus the U.S. war effort from Iraq to Afghanistan.

Due to the surge, the officials told reporters, the military mission in Afghanistan has made great progress toward its objectives of dismantling and defeating al Qaeda in the region while stabilizing the country to prevent it from again being a safe haven for terrorist attacks on the United States.

The killing of bin Laden in early May and the success in reversing Taliban momentum in the southern provinces of Helmand and Kandahar enabled the beginning of a troop withdrawal that will culminate with handing over security responsibilities to Afghan forces in 2014, the senior administration officials said on condition of not being identified.

Gates -- along with Afghan war commander Gen. David Petraeus -- had pushed for an initial drawdown of 3,000 to 5,000 troops this year, according to a congressional source. Gates also urged the president to withdraw support troops only -- not combat troops.

Obama, however, ultimately decided to adopt a more aggressive withdrawal plan. The senior administration officials said Obama's withdrawal schedule fell within the range of options presented to him by Petraeus, who has been nominated to become CIA director to succeed Leon Panetta, who will take over as defense secretary when Gates steps down at the end of the month.

In a statement after Obama's speech, Gates said it was "critical" that U.S. forces continue to "aggressively" carry out the surge strategy of degrading the capability of the Taliban while bolstering Afghan security forces.

"I support the President's decision because it provides our commanders with enough resources, time and, perhaps most importantly, flexibility to bring the surge to a successful conclusion," Gates said, signaling Pentagon control in deciding which U.S. forces withdraw.

Earlier this week, Gates acknowledged that the president must take into account public opinion and congressional support for further military engagement.

"Sustainability here at home" is an important consideration, Gates said, noting that people are "tired of a decade of war."

Public exhaustion with the conflict is reflected in recent public opinion polls. Nearly three-quarters of Americans support the United States pulling some or all of its forces from Afghanistan, according to a June 3-7 CNN/Opinion Research Corp. survey.

That figure jumped 10 percentage points since May, likely as a result of the death of bin Laden, pollsters said.

Republicans -- who have been the strongest supporters of the U.S. military presence in Afghanistan -- are shifting their opinion on the conflict. In May, 47% of Republicans said they favored a partial or full withdrawal of American troops. That figure rose to 60% this month.

The sharp divisions have been reflected in Congress, where both Democrats and Republicans are increasingly split.

Sen. Joe Manchin, D-West Virginia, called Tuesday for a "substantial and responsible reduction" in troop levels, arguing the war has become fiscally irresponsible and more resources need to be focused on domestic problems.

The United States has spent roughly $443 billion on the war in Afghanistan, according to budget analysts. According to Travis Sharp, a researcher at the Center for a New American Security, the troop reductions Obama announced would bring a savings of about $7 billion in fiscal year 2012.

CNN's Aliza Kassim, Barbara Starr, Ted Barrett, Deirdre Walsh, Tom Cohen, Alan Silverleib and Brianna Keilar contributed to this report.