The Boston Athletic Association (B.A.A.) is hosting the 2008 U.S. Olympic Team Trials for the Women's Marathon. The top three finishers will go to Beijing this summer as members of the U.S. Olympic Team. More than 150 elite female marathoners have qualified for the trials, including 14 New Englanders and 2004 Olympic bronze medalist Deena Kastor. Participants will complete four loops of approximately six miles each through Back Bay, across the Charles River and into Cambridge.