WASHINGTON, Jan 25 (Reuters) - Republican U.S. Senator Saxby Chambliss of Georgia will not run for a third term in 2014, a congressional aide said on Friday, potentially leaving Congress with one less Republican who was willing to sit down with Democrats on fiscal issues. Chambliss, who rebelled against anti-tax lobbyist Grover Norquist by saying he was open to raising taxes, was being targeted by conservative Tea Party members in Georgia. No one had announced a challenge to Chambliss.