NORMAN, Okla. - University of Oklahoma wrestling head coach Jack Spates has signed Johnny Galloway Jr., a three-time Iowa state champion, to a national letter of intent. Galloway will be a freshman at OU next fall.    Galloway is ranked fifth nationally in the 160-pound weight class by Intermat and seventh by Amateur Wrestling News. The Iowa City High School senior had a spectacular prep career, going 153-9 over his four years. He cruised to the state title this past year with the closest match of the state meet being a 16-6 major decision over a previously undefeated Grant Turner in the finals.    "Johnny Galloway is a tremendous challenge for his opponents," said Spates, "and we expect him to make a quick transition into college wrestling. He is an explosive athlete with good technique that comes from a good Iowa program. He is a good kid and we couldn't be more happy to have him in our Oklahoma program."