WASHINGTON (Reuters) - Even before US President Barack Obama decides to send more combat troops to Afghanistan, many members of his own party are resisting it, with experts saying the president must do a better job to sell his plans. When Obama announced his review of Afghanistan strategy last March, most Democratic lawmakers lined up to endorse his efforts. But scepticism is now creeping in, with firmer support coming more from Republicans than his own base. This puts the president in the middle between his own supporters and his Republican critics who are going to look for any sign of softening resolve as a sign that the president is going weak on terrorism, said Bruce Riedel of the Brookings Institutions Saban Centre. To stem this tide of scepticism, which is also reflected in US public opinion polls, experts say Obama must work harder to promote his strategy - much as he has done in recent weeks to push an overhaul of the US healthcare system. We are getting to a turning point here. We are going through a bit of an existential crisis, said Karin von Hippel of the Centre for Strategic and International Studies, a Washington think-tank. Von Hippel said Obama would have to find a way to manage growing concerns on Capitol Hill, while encouraging debate among a public increasingly disenchanted with the war in Afghanistan, where insurgent violence has reached its highest level since the Taliban was ousted from power in late 2001. I hear more support for Afghanistan from soldiers than I do from American civilians, von Hippel said. Riedel, who oversaw the March review of Afghanistan and Pakistan strategy, anticipated a presidential speech soon during which Obama would again lay out his case for why a fully resourced effort was imperative in Afghanistan. Obama is considering a formal assessment of the war from Gen Stanley McChrystal, the top US and Nato commander in Afghanistan, whose report is expected to result in a request by the military for more combat forces. Afghanistan is starting to look like a long-term conflict in which the end and how we are going to get there is not clear to a lot of people, said Alex Thier, an expert on Afghanistan from the US Institute of Peace. The administration definitely needs to be more forceful in its justification for not only being involved in Afghanistan today but why this is a longer-term challenge, said Thier. The White House has sought to play down congressional discord over troop levels but there appears to be growing internal debate over what to do next, with Obamas press secretary, Robert Gibbs, saying it could now take many, many weeks before announcements on troop changes are made. House of Representatives Speaker Nancy Pelosi sounded alarm bells last Thursday when she said Congress would probably not back a call for any more combat troops. A day later, Michigan Senator Carl Levin, Democratic chair of the Armed Services Committee, said the focus should be on boosting Afghan troop levels and not sending more US forces. In contrast, most Republicans say they would favour giving US military commanders more troops if they want them. It would be a strategic mistake - and a disservice to the men and women whove put their lives on the line - to do otherwise, said John Boehner, head of the House Republicans. Representative Howard McKeon from California, the top Republican on the House Armed Services Committee, also said holding back on resources would be a major error and could lead to defeat. Another complicating factor for Obama as he decides troop levels is the political uncertainty in Afghanistan following the countrys inconclusive August election where allegations of fraud are rampant. Karzai needs to understand that everyone could pull the plug. The Afghan people need to put a lot more pressure on him too, said von Hippel.