Bronx residents and elected officials gathered Monday in their fight to keep the Westchester Square Medical Center from closing. The center is believed to be one of six city hospitals a state commission wants to close to cut costs. The hospital employs 600 workers who treat an average of 23,000 emergency cases each year. Many say closing the hospital would be a disservice to the entire borough. If Westchester Square is forced to close, it may merge with its affiliate, New York Presbyterian Hospital. The commission is expected to release the list of hospitals on Tuesday.