Leading up to the president's announcement, the White House stressed again that it would not involve any re-tooling of the strategy unveiled in December 2009 in a speech Mr. Obama delivered at the U.S. military academy at West Point, New York.

    In that address, Mr. Obama set out what he called a "strategy to bring this war to a successful conclusion" and announced deployment of an additional 30,000 troops aimed at turning back Taliban advances.

    "As commander in chief I have determined that it is in our vital national interest to send an additional 30,000 U.S troops to Afghanistan.   After 18 months our troops will begin to come home.  These are the resources that we nee to seize the imitative while building the Afghan capacity that will allow for a responsible transition of our forces out of Afghanistan," Mr. Obama said.

    At the time, Mr. Obama noted the war's "enormous costs in lives and resources" but said he was convinced that U.S. security was at stake in what he called the epicenter of violent extremism in Afghanistan and Pakistan.

    The president will reaffirm his commitment from 2009 to begin withdrawing forces.   Various reports quoted administration officials as saying at least 5,000 soldiers, about one brigade, could come out in coming months, with another by the end of the year.

    Cautioning against media speculation, White House Press Secretary Jay Carney said Mr. Obama has remained focused on three objectives:  disrupting, dismantling and defeating al-Qaida, reversing Taliban momentum, and preventing Afghanistan from becoming a safe haven for terrorists.

    "Those objectives are being met, we have had a significant amount of success in meeting those objectives and the president has been very engaged in the process evaluating that.  We are not there yet obviously, but it is important to remember what the objective were from the beginning and what they were not and the president will make that clear again tomorrow evening," Carney said.

    Mr. Obama will reiterate the U.S. and NATO commitment of completely transferring security responsibilities to Afghan government forces by 2014.   He and military commanders have stressed that the speed of withdrawals would be based on conditions on the ground.  Withdrawal of the 30,000 U.S. surge force by next year would still leave some 68,000 U.S. troops in Afghanistan.

    The president could also address growing anti-war sentiment in the United States, reflected in public opinion polls, and positions taken by members of Congress.

    In the U.S. Senate, Democrat Joe Manchin of West Virginia made the case heard more frequently that the U.S. can no longer afford the costs of the Afghanistan war.  Republican John McCain responded.

    MANCHIN: "The question the president faces and we all face is quite simple.  Will we choose to rebuild America, or Afghanistan?"MCCAIN: "If we leave Afghanistan in defeat, we will repeat the lessons of history, and it is not our expenditures on Afghanistan that are the reasons why we are now experiencing the budget difficulties that we are experiencing."Before a meeting with President Obama on Tuesday, outgoing Secretary of Defense Robert Gates told reporters Mr. Obama clearly had to take American's concerns about war costs into account in making his decision, in addition to conditions on the ground in Afghanistan.

    "It goes without saying that there are a lot of reservations in the Congress about the war in Afghanistan and our level of commitment.  There are concerns among the American people who are tired of a decade of war," Gates said.

    One day after announcing his Afghanistan troop decision, President Obama will visit the military base at Fort Drum, New York, home to the 10th Mountain Division, which has seen intense and frequent deployments in Afghanistan as well as Iraq.（本文由在线英语听力室整理编辑）