New York City's Health & Hospitals Corp., the nation's largest public hospital system, plans to stanch a $1.2 billion budget gap in the next year's budget by laying off about 500 workers and ending contracts with "a significant number" of physicians, its president said. While HHC says the plan would affect all employee groups, the most seriously affected would be administrative managers and trades employees, many of whom work to keep buildings running, said Alan Aviles, HHC's president.