THE Obama administration is holding off major decisions that could put its military forces on a firmer war footing in Afghanistan even as doubts grow about whether the United States can win there. Many military and diplomatic leaders have urged President Barack Obama to send thousands more Marines, soldiers and pilots to try to reverse Afghanistan's crumbling security situation. But White House spokesman Robert Gibbs has said no decision about adding troops is expected for “weeks and weeks,” following what he described as intensive evaluation. The troop decision will be a first indicator of whether Obama intends to increase American military involvement in Afghanistan, becoming a wartime president in earnest. Leading Democrats in Congress have signaled they do not support a troop increase now, and maybe not at all. The chairman of the Joint Chiefs of Staff, Adm. Mike Mullen, has the unhappy task of telling the Senate Armed Services Committee Tuesday why the United States should stay the course and commit to what he calls a “properly resourced counterinsurgency effort.” Mullen's long-scheduled nomination hearing for a second term as the president's chief military adviser will be chaired by Sen. Carl Levin of Michigan, who warned the White House last week not to push for a big troop increase. He wants the Pentagon to focus on quicker training for Afghan security forces instead. Mullen has sounded increasingly alarmed about the growing technical capabilities of a resurgent Taleban and about the lackluster support among Afghans for the foreign-run enterprise that purports to protect them from a homegrown insurgent movement. “Time is not on our side,” Mullen said this month. Postponing whether to add more American forces and alter other aspects of military strategy could give the White House breathing room for other priorities, including a health care overhaul and a hard-fought defense budget package. Leading congressional Republicans, who have become Obama's strongest supporters for the Afghan effort, are fretting that he will punt. Republican Sens. John McCain of Arizona and Lindsey Graham of South Carolina, and Sen. Joseph Lieberman of Connecticut, an independent, warned in a Wall Street Journal essay Monday that muddling through is a recipe for disaster. “More troops will not guarantee success in Afghanistan, but a failure to send them is a guarantee of failure,” they wrote. Recent national polls indicate slipping support for the nearly eight-year war and growing doubt that it can be won. The latest AP-GfK survey finds that fewer than half — 46 percent — now approve of Obama's handling of Afghanistan, a 9 percentage point drop since July. A CNN poll conducted in the final four days of August said 42 percent supported the war and 57 percent opposed it. That compared with 53 percent supporting and 46 percent opposing in early April, days after Obama announced a new war strategy and vowed to provide resources to the war effort in ways his predecessor had not. “I just don't know that more troops is the answer,” Republican Sen. Susan Collins of Maine, said Sunday on CNN. She is also a member of the Senate Armed Services Committee. “I'm just wondering where this ends and how we'll know if this succeeded,” Collins said. Gen. Stanley McChrystal, the top US commander in Afghanistan, is widely expected to ask for more forces for what he describes as a nearly complete do-over of the Bush administration's strategy to fight an increasingly unpopular war. That request is expected within two weeks, following a summer-long review and a classified assessment of the prospects for applying the revamped counterinsurgency strategy that Obama outlined earlier this year. Congressional defense leaders are due to be briefed this week on McChrystal's assessment, which was the subject of a White House meeting with top military leaders Sunday.