Washington • President Barack Obama declared Wednesday that the United States had largely achieved its goals in Afghanistan, setting in motion a timetable for the rapid withdrawal of U.S. troops in an acknowledgment of the shifting threat in the region and fast-changing political and economic landscape in a war-weary America.

Asserting that the country that served as a launching pad for the Sept. 11, 2001 attacks no longer represented a terrorist threat to the United States, Obama declared that the "tide of war is receding." And in a blunt acknowledgment of domestic economic strains, he said, "America, it is time to focus on nation-building here at home."

Obama announced plans to withdraw 10,000 troops from Afghanistan by the end of this year. The remaining 20,000 troops from the 2009 "surge" of forces would leave by next summer, amounting to about a third of the 100,000 troops now in the country. He said the troop reductions would continue "at a steady pace," bringing to an end America's longest war — a conflict that has cost 1,500 American lives.

The troop reductions, which came after a short but fierce internal debate, are both deeper and faster than the recommendations made by Obama's military commanders, and they come as the president faces relentless budget pressures, an increasingly restive Congress and U.S. public and a re-election campaign next year.

The withdrawals would mark the start of a winding down of the military's counterinsurgency strategy, which Obama adopted 18 months ago. Most U.S. forces are expected to leave Afghanistan by 2014. Administration officials indicated that they now planned to place more emphasis on smaller, focused counterterrorism operations of the kind that killed Osama bin Laden, which the president cited as Exhibit A in the case for a substantial U.S. troop reduction.

"We are starting this drawdown from a position of strength," Obama said in a somber, 12-minute address delivered from the East Room of the White House. "Al-Qaida is under more pressure than at any time since 9/11." He said that an intense campaign of drone strikes and other covert operations in Pakistan had crippled al-Qaida's original network in the region, leaving its leaders either dead or pinned down in the rugged border between Pakistan and Afghanistan. Of 30 top al-Qaida leaders identified by U.S. intelligence, 20 have been killed in the last year and a half, administration officials said.

But the withdrawal of the entire surge force by the end of next summer will significantly change the way that the United States wages war in Afghanistan, analysts said, suggesting that the administration may have concluded it can no longer achieve its loftiest ambitions there.

Obama acknowledged as much in his remarks. "We will not try to make Afghanistan a perfect place," he said. "We will not police its streets or patrol its mountains indefinitely. That is the responsibility of the Afghan government."

Obama's decision is a victory for Vice President Joe Biden, who has long argued for curtailing the military engagement in Afghanistan. The president signaled that the days of the United States responding to terrorist attacks with massive force were over, and indicated a willingness to move toward more focused clandestine operations of the type that the United States is conducting in Pakistan, Yemen, and elsewhere. "When threatened, we must respond with force," he said. "But when that force can be targeted, we need not deploy large armies overseas."

The pace of the withdrawal is a setback for his top commander in Afghanistan, Gen. David H. Petraeus, who has been named director of the CIA. Petraeus, who helped write the Army's field manual on counterinsurgency policy, did not endorse the decision, said another official, though both Defense Secretary Robert M. Gates and Secretary of State Hillary Rodham Clinton both accepted it with reservations.

Petraeus had recommended limiting withdrawals to 5,000 troops this year and another 5,000 over the winter, deferring the withdrawal of the rest of the surge force through next year's fighting season.

He and other military commanders argued that the 18 months since Obama announced the troop increase did not allow for enough time for the Americans to consolidate the fragile gains that they had made in Helmand and other provinces. Military officials say the withdrawal of U.S. troops will impose limits on which areas of the country can be pacified. In particular, plans to pivot extra U.S. troops from south and southwestern Afghanistan to volatile areas in the east, along the Pakistan border, will be curtailed or even canceled, officials said.

Troops have succeeded in clearing many towns and cities of insurgents, and then keeping them safe so that markets reopened and girls were able to go to school, for example.

But the effort to transfer responsibility for security to Afghan forces remains elusive because the Afghan troops are proving unprepared for the job.

While senior administration officials said Wednesday that the military campaign had made Afghans better able to govern themselves, they cited few specific initiatives that showed the Afghan government taking more responsibility for its citizens' security. Corruption in the government of President Hamid Karzai continues to be rampant, sapping the confidence of many Afghans.

Still, the growing disenchantment at home with the war, particularly given the ballooning national debt, the country's slow economic recovery, and the whopping $120 billion price tag of the Afghan war this year alone, were all considerations weighed by the president.

"Over the last decade, we have spent a trillion dollars on war at a time of rising debt and hard economic times," Obama said. "Now, we must invest in America's greatest resource: our people."

Even some Republicans have been getting on the get-out-of-Afghanistan bandwagon. Republican presidential hopefuls including Mitt Romney and Jon M. Huntsman are demanding a swift withdrawal from Afghanistan, while Democrats on Capitol Hill and elsewhere complain that the cost of the war is siphoning money away from efforts to create jobs in the United States.

Rep. Dana Rohrabacher, R-Calif., called on Obama to speed the withdrawal on Wednesday. "If we're going to leave, we should leave," he said in a statement. "The centralized system of government foisted upon the Afghan people is not going to hold after we leave. So let's quit prolonging the agony and the inevitable."

Highlighting the unusual political splits the war is causing, other Republicans criticized the president for pulling out too soon.

Mike Rogers, the Michigan Republican who is chairman of the House Intelligence Committee, suggested that Obama was playing politics with the troop reduction, saying, "The president is trying to find a political solution with a military component, when it needs to be other way around." He said the situation in Afghanistan was "very precarious," and that the White House seemed to be panicking about the levels of violence. —

By the numbers: Afghanistan

100,000

U.S. troops now in Afghanistan

1,500

Number of U.S. lives lost in the country's longest war

10,000

Number of U.S. troops to be pulled out of Afghanistan by the end of 2011

20,000

The remainder of 2009 "surge" forces to leave by summer of 2012