WASHINGTON, Nov. 12 (Xinhua) -- Amid speculations on U.S. President Barack Obama's final decision on a pending troop buildup in Afghanistan, U.S. Defense Secretary Robert M. Gates hinted Thursday that U.S. military presence in that country is not open-ended.

    Talking to reporters aboard a plane en route to Oshkosh, Wisconsin, Gates said Obama's decision, which White House said is still weeks away, would "signal to the Afghans as well as to the American people that this isn't an open-ended commitment."

    He also said the president is "picking the best ideas" among troop buildup options that his top aides presented to him on Wednesday.

    Analysts said Gates' words illustrated the Obama administration's concern that a troop buildup in Afghanistan would further alienated voters at home, who are growingly annoyed by the prospect of an open-ended war in Afghanistan.

    Earlier in the day, a senior administration official who spoke on the condition of anonymity, said that Obama is trying to establish an exit strategy before committing to sending a significant number of U.S. troops to Afghanistan.

    That was apparently aimed to ease Americans' concerns on the Afghan war as latest poll results show as much as 58 percent of Americans oppose the war.

    Obama is in the final stages of a months-long review of his Afghan strategy and was given four options by his top aides.

    All the options include an element of troop increase in Afghanistan.

    U.S. officials said Thursday that the president asked his top aides to revise the four options "to clarify how and when U.S. troops would turn over responsibility to the Afghan government."