An Amtrak train headed to Chicago hit a semitrailer that was stuck on the tracks in southern Michigan on Wednesday, leaving 10 people injured according to authorities.   It is reported that Amtrak said the engine came to rest on its side and the first two train cars derailed in the incident in Leoni Township, 45 miles south of Lansing. The train, which began its trip in Pontiac, north of Detroit, had been carrying 68 passengers and five crew members.   The Associated Press reports seven passengers, the truck driver, the train engineer and another Amtrak employee were injured.  None with life-threatening injuries.  The truck was carrying equipment for local oil production and got hung up on the tracks while trying to cross.  The track is expected to be operational again sometime this morning.