There is no larger employer in the world than the United States Government. Positions are available on a near regular basis, despite recent cutbacks. Not only are there opportunities domestically, but employment outside the United States is a possibility on military bases, overseas embassies and various departments of defense and state agencies.
You will have to become familiar with a whole new employment language. This is the federal government, after all. A special occupational classification system exists which determines pay and job grades.