Sammy Morris, running back for the Miami Dolphins, is expected to return to work today after a four-game absence as a result of a failed drug test. During a conversation with his agent Saturday, Morris said he has been running and working out in Miami since his departure from the Dolphins on Sept. 2. Morris, who suffered a slight foot sprain, has recovered. ''He can't wait to get back,'' said Mark Slough, who represents Morris. ``He's definitely ready to go.''