WASHINGTON (Reuters) - President Barack Obama may pick Army Chief of Staff General Martin Dempsey as the US militarys top officer, filling a crucial post that in recent years has served as the main point of contact with Pakistans military, sources said on Wednesday. General Dempsey is a leading candidate for the high-profile job of chairman of the US militarys Joint Chiefs of Staff, according to the sources, who spoke on condition of anonymity. Dempsey, who commanded troops during the Iraq war and has broad support in Congress, would replace Admiral Mike Mullen in the post. Mullen is a holdover from the Bush administration who has been in the role of top US military officer since 2007 and is due to step down on Oct 1. As army chief of staff, Dempsey is the top officer in the largest branch of the US military. He has served in the post only since last month. The nomination of Dempsey would be the last major change expected in Obamas national security team following the presidents April announcement of new picks to lead the Defence Department and the CIA. If confirmed, Dempsey would work with Leon Panetta, now the head of the CIA and Obamas choice to replace the departing Robert Gates as defence secretary. Obama picked Army General David Petraeus, commander of the Afghanistan war effort, to replace Panetta at the spy agency. Dempseys selection would alter the chemistry of a team that will help set strategy in Afghanistan, the Middle East and for looming defence budget battles in Washington. He also would be involved in plans to withdraw US forces entirely from Iraq by the end of this year. General James Cartwright, the current vice chairman of the Joint Chiefs of Staff, had been considered the favourite to replace Mullen but Obama informed him on Saturday he was not chosen for the job, a US official said, speaking on condition of anonymity. The official said one concern was that neither Mullen nor Gates had endorsed Cartwright for the job, the official said.Some top brass have complained in the past about Cartwrights leadership style.