ARLINGTON, Va. - (AP) - President Barack Obama paid tribute Monday to the men and women who have died defending America, saying the country must strive "to be a nation worthy of your sacrifice." He said the war in Iraq has ended after nine years and is "winding down" in Afghanistan. But he conceded that the pain of war lingers for the families of those lost in battle, noting mourners can be seen daily at Arlington National Cemetery daily, not just on Memorial Day. "These 600 acres are home to Americans from every part of the country who gave their lives in every part of the globe," said the president, speaking under a brilliant sun before a large audience, including many uniformed servicemen and women, at the cemetery, after taking part in the traditional laying of a wreath at the Tomb of the Unknowns. The president promised war veterans that "we will be there for you," to ensure that troops returning home from battle get the benefits they deserve. Preceding Obama, Defense Secretary Leon Panetta said that "all the men and women who rest here are a constant reminder that freedom is not free." He noted that some 6,400 men and women have died defending America since the terror attacks of Sept. 11, 2001.