In a divorce petition filed in Bexar County, Tex., in late June, 34-year-old Sonia Lo Duca accuses Paul Lo Duca of infidelity. Yet sources close to the Brooklyn-born four-time All-Star told The News that his divorce fight was only part of his woes. The sources said Lo Duca also had gambling debts, accumulating a big enough tab that Mets management was aware of it. The morals clause within Major League Baseball doesn't prohibit a player from gambling at casinos or race tracks, but the league becomes concerned when one of its players runs up unmanageable gambling debts. Lo Duca insisted to The News on Monday that he only gambled on horses, never on sports. He admitted betting through the Internet, but said all his wagers were legal.