The new deployments, to begin in May, will increase the U.S. force in Afghanistan by nearly 50 percent, bringing it to 55,000 by mid-summer, along with 32,000 non-U.S. NATO troops. In a statement issued by the White House, Obama said that "urgent attention and swift action" were required because "the Taliban is resurgent in Afghanistan and al-Qaeda . . . threatens America from its safe-haven along the Pakistani border."

Taliban attacks and U.S. and NATO casualties last year, including 155 U.S. deaths, reached the highest levels of the seven-year war. War-related civilian Afghan deaths -- most blamed on Taliban insurgents but many on U.S. airstrikes -- increased nearly 40 percent to 2,118 in 2008, according to a U.N. report released yesterday. Extremist groups have expanded their hold on western Pakistan and launched terrorist attacks in major Pakistani cities.

Months ago, the commander of U.S. and NATO forces in Afghanistan, Gen. David D. McKiernan, requested more than 30,000 additional troops this year, and an initial 6,000 arrived last month under orders signed by the Bush administration. But a senior White House official said that no other deployment decisions will be made until the Obama administration completes a strategic review of the Afghan war in late March.

Obama has said he wants to limit U.S. objectives in Afghanistan, and administration officials have spoken of a more "regional" counterinsurgency strategy, including expanded assistance to Pakistan and diplomatic outreach to India, Iran, Russia and other neighboring countries.

Afghan President Hamid Karzai was informed of the new deployments in a telephone call from Obama yesterday. Karzai, whose government Obama criticized last week as "detached" from what is going on in Afghanistan, publicly complained over the weekend that he had not yet heard from the new U.S. president.

The first additional U.S. contingent, the 8,000-strong 2nd Marine Expeditionary Brigade from Camp LeJeune, N.C., will arrive in late May. The Army's 5th Stryker Brigade, 2nd Infantry Division from Fort Lewis, Wash., will arrive with 4,000 troops in late July, along with an additional 5,000 troops in still-undesignated smaller units.

The new troops will move into southern and eastern Afghanistan for combat expected to increase with the arrival of warmer weather, in addition to providing additional training for the Afghan army and security for national elections scheduled for August. Obama also plans to ask NATO to supply additional resources this year.

The administration sought yesterday to couch the orders as what the senior official called "the beginning of the drawdown of troops in Iraq," where both units had been scheduled to deploy. While that is technically true, White House decisions on Afghanistan and Iraq are proceeding on parallel but not necessarily overlapping tracks.

During the presidential campaign, Obama pledged to drawn down the U.S. presence in Iraq -- currently at 146,000 troops -- at a rate of one brigade a month for what he said would be a complete combat withdrawal within 16 months, with an unspecified "residual force" remaining.

During his first week in office, he instructed military planners to present options for withdrawal under various conditions on the ground and at various speeds. Those options have not yet been presented to the White House, although the senior official said yesterday that Obama expects to receive them and make a decision on a timeline "in the near future."

The situation in Afghanistan and Pakistan has been discussed in separate presidential meetings with top national security and military officials who are contributing to the strategic review. In the meantime, however, commanders warned that deployment decisions would have to be made now if troops were to arrive in Afghanistan in time to meet urgent security needs.

Obama recognizes that "there is a grave situation in certain parts of the country," the White House official said. "We know . . . how negative it would be if the elections didn't come off. It's also well acknowledged that the effort in Afghanistan suffered [under Bush] from being under-resourced, with a lack of attention and strategic direction."

White House spokesman Robert Gibbs said yesterday that the deployment decision "does not prejudge the outcome of the review process but . . . allows us instead to meet an urgent need for more troops."

Beginning his first week in office, Obama held a series of meetings on the subject with civilian and military officials, including McKiernan; Gen. David H. Petraeus, head of U.S. Central Command; Adm. Michael Mullen, chairman of the Joint Chiefs of Staff; Defense Secretary Robert M. Gates; and Secretary of State Hillary Rodham Clinton.

On Feb. 10, Gates recommended that Obama authorize the 17,000-troop deployment. The recommendation was discussed at a National Security Council meeting Friday, and Obama informed Gates of his decision Monday. Gates signed the deployment orders for the 12,000 troops of the two brigades yesterday, with designation of the additional 5,000 still to come.

"This administration has a different way of doing business," said a Pentagon official who also served under Bush. "The Obama White House wants to go about this in a much more methodical way than its predecessor, with decisions about troop levels to be evaluated by more than the military chain of command."

Obama's deployment decision came without clear majority support from the public. While most Americans consider winning in Afghanistan essential to victory in the broader fight against terrorism, in the latest Washington Post-ABC News poll, barely more than a third, 34 percent, said the number of U.S. military forces in that country should be increased. About as many would opt for a decrease (29 percent) or no change at all (32 percent).

In Afghanistan, public opinion is even more unwelcoming. In a recent ABC-BBC-ARD poll of Afghans, just 18 percent said the United States and NATO should increase their troop levels, and more than twice that number, 44 percent, wanted fewer outside forces.

Yesterday's U.N. report, along with a separate report on Afghanistan by the independent Campaign for Innocent Victims in Conflict (CIVIC), noted that rising civilian casualties are the source of deep resentment among the Afghan public. Although the United Nations said that "anti-government elements" were responsible for 55 percent of last year's civilian deaths, CIVIC reported that "the international coalition in Afghanistan is losing public support, one fallen civilian at a time."

The CIVIC report noted that the United States and NATO governments all pay compensation to some civilian victims of their actions -- although there is no coordinated system, and many families receive nothing -- and recommended that such efforts be improved and expanded.

Polling director Jon Cohen contributed to this report