Gunfire erupted in the storied Waldorf-Astoria Hotel during a brazen robbery attempt Saturday at a lobby jewelry store, wounding a security guard and sending guests diving for cover. The 54-year-old guard was shot in the chest but was expected to survive, and a suspect was in custody, police said. Charges were pending. Hotel guest Christine Cataldo said she was looking at a display of engagement rings near the entrance to the store, Cellini Jewelers, when she heard the first shot. "It sounded like a bomb. One big boom. And then people started running," said Cataldo, of Long Island. "I looked up, and I saw a man in a suit with silver hair grabbing another guy." The mayhem began when the 20-year-old suspect, wearing a black track suit, pulled out a gun in the jewelry store and used the weapon to smash two display cases full of expensive rings and necklaces, said a police official who spoke on condition of anonymity because detectives were still investigating.