Louise Seng had as big a stake as anyone in what President Bush said in his State of the Union address Tuesday night. As the wife of an Army reservist who is waiting at Fort Dix, N.J., to be deployed, and the mother of a 21-year-old Marine whose ship is somewhere in the Atlantic Ocean and probably headed toward the Middle East, Seng had a lot riding on what George Bush had to say about the United States being on the brink of war with Iraq.