U.S. Defense Secretary Robert Gates has acknowledged concerns in the United States about the war in Afghanistan, saying the American people are “tired of a decade of war.”

Gates spoke in Washington Tuesday, one day before President Barack Obama is expected to announce his plans for withdrawing U.S. troops from Afghanistan.

The defense chief said the president has to take into account sustainability at home, both in Congress and among the American public, as well as conditions on the ground in Afghanistan.

A senior administration official said Mr. Obama will outline both a plan to start bringing home some of the 100,000 U.S. troops beginning in July, and future withdrawals aimed at giving Afghans control of their own security by 2014.

There is growing U.S. public dissatisfaction with the Afghan war, caused by concern about the number of U.S. casualties and the effect of the cost of the war on the U.S. economy.

Gates said there are “a lot of reservations” in Congress about the war and the level of U.S. commitment.

Gates was speaking at the State Department, before heading to the White House with Secretary of State Hillary Clinton for consultations with the president about Afghanistan.

Mr. Obama announced the July start for the withdrawal in December 2009, when he presented his overall strategy for Afghanistan.