Oregon officials have suspended 10 recent and upcoming timber sales on about 800 acres of state land as they prepare for a legal fight with conservation groups over a rare seabird.   The question in that battle is whether the state's logging goals in the coastal Elliott, Tillamook and Clatsop State Forests illegally harm the habitat of the threatened Marbled Murrelet, which is protected under the Endangered Species Act.   The bird lays its eggs on the large, mossy branches of mature and old-growth trees.  Oregon Forestry Department spokesman Kevin Weeks says the state took the unprecedented action so that officials who would normally work on timber sales could focus on preparing for the federal court fight in Portland.  In May, 3 environmental groups sued Governor John Kitzhaber and Oregon Forestry agencies in an effort to halt logging in areas where the bird nests.