The largest union of nurses in New York City is voicing dismay that contracts at four large hospitals have expired without a new agreement being reached. The nurses believe that the hospitals--St. Vincent's Hospital Manhattan, St. Luke's-Roosevelt hospitals and NewYork-Presbyterian/Columbia--should be generous in their contract offers in light of the nationwide nursing shortage. Michael Fraser, a spokesman for the Healthcare Association of New York State, said it was hard for hospitals to pay nurses more even though the nursing shortage was expected to grow worse.