WASHINGTON (AP) — Charting an end to America's longest war, President Barack Obama announced plans Tuesday for keeping nearly 10,000 U.S. troops in Afghanistan after this year but then withdrawing virtually all by the close of 2016 and the conclusion of his presidency.

The drawdown would allow Obama to bring America's military engagement in Afghanistan to an end while seeking to protect the gains made in a war in which he significantly intensified U.S. involvement.

"We have to recognize that Afghanistan will not be a perfect place, and it is not America's responsibility to make it one," Obama declared during an appearance in the White House Rose Garden.

He credited American forces, which were first deployed by President George W. Bush within a month of the Sept. 11, 2001, attacks, with striking significant blows against al-Qaida's leadership, eliminating Osama bin Laden and preventing Afghanistan from being used as a base for strikes against the U.S. He said: "Now we're finishing the job we've started."

The drawdown blueprint is contingent on Afghanistan's government signing a stalled bilateral security agreement. While current Afghan President Hamid Karzai has refused to sign the accord, U.S. officials say they're confident that either of the candidates running to replace him will finalize the deal.

In fact, both candidates who are on the ballot in next month's runoff — former Foreign Minister Abdullah Abdullah and ex-Finance Minister Ashraf Ghani Ahmadzai — welcomed Obama's announcement Tuesday. But not everyone at home did.

The size and scope of the residual U.S. force largely mirrors what Pentagon officials had sought, which appeared to give Obama cover with some Republicans, including House Speaker John Boehner, R-Ohio. But some of president's harshest critics on foreign policy — Sens. John McCain of Arizona, Lindsey Graham of South Carolina, and Kelly Ayotte of New Hampshire — called the decision short-sighted and warned that it would embolden enemies.

"The president's decision to set an arbitrary date for the full withdrawal of U.S. troops in Afghanistan is a monumental mistake and a triumph of politics over strategy," the three Republicans said in a joint statement.

U.S. forces had already been on track to stop combat operations in Afghanistan by the end of 2014, more than 13 years after the American-led invasion. But Obama wants to keep some troops there to train Afghan security forces, launch counterterrorism missions and protect progress made in a war that has left at least 2,181 Americans dead and thousands more wounded.

There are currently about 32,000 U.S. troops in Afghanistan. Under Obama's plan, that number would be reduced to 9,800 by the start of 2015, dispatched throughout Afghanistan.

Over the course of next year, the number would be cut in half and consolidated in the capital of Kabul and at Bagram Air Field, the main U.S. base in Afghanistan. Those remaining forces would largely be withdrawn by the end of 2016, with fewer than 1,000 remaining to staff a security office in Kabul.

The American forces would probably be bolstered by a few thousand NATO troops.

Noting the complexity of his drawdown plan, Obama said, "It's harder to end wars than to begin them."

The formal end of the Afghan war has triggered a White House effort to reframe America's foreign policy after more than a decade of conflict. During a commencement address Wednesday at the U.S. Military Academy at West Point, Obama is expected to make the case for an approach to global problems that relies on international consensus.

The U.S. tried to keep a residual force in Iraq as combat missions there came to an end, but Washington and Baghdad were unable to finalize a security agreement. In the vacuum left by the American military, Iraq has been battered by resurgent waves of violence.

The president is seeking to avoid a similar scenario in Afghanistan, for both security and political purposes. While Obama long opposed the Iraq war, he oversaw a surge of U.S. forces in Afghanistan, giving him greater responsibility for the mission's success or failure.

Even Obama has at times been skeptical of the prospects for success there. But he struck an optimistic tone during a surprise visit to Afghanistan on Sunday, telling military commanders that the process of turning over security responsibilities has gone "better than I might have expected just a year ago."

U.S. officials have also been buoyed by the successful start of the Afghan presidential elections, which will conclude next month.

Ahead of his remarks, Obama spoke with Karzai, who has had a tumultuous relationship with the White House. The two leaders did not see each other while Obama was in Afghanistan, but they did speak by phone as Air Force One was returning to Washington.

Obama has also discussed his plans with several European leaders, including German Chancellor Angela Merkel, British Prime Minister David Cameron and Italian Prime Minister Matteo Renzi.

As the military draws down in Afghanistan, the CIA also will gradually close its bases along the Pakistan border and pull most of its officers back to the capital, U.S. officials say. While the CIA uses its own private security force to guard its bases, it relies on the military for transport, logistics and emergency medical evacuation, and the civilian spy agency is not willing to risk a significant deployment of officers in rural Afghanistan without U.S. troops nearby, the officials say.

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Associated Press writers Lolita C. Baldor, Ken Dilanian and Donna Cassata in Washington and Amir Shah in Kabul, Afghanistan, contributed to this report.

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