A city Parks Department employee accused of killing a co-worker as they argued over a plastic trash bag was indicted yesterday on murder charges.

Robert Swann, 51, was arraigned in Queens Supreme Court. He allegedly picked up a knife near a work shed at the Queens Zoo in Flushing Meadows Park and stabbed Ezra Black, 31, in the stomach on Sept. 4. They had been colleagues for five months.

Defense attorney Michael Siff entered a not-guilty plea on behalf of his client, who allegedly tried to discard the knife and his bloody work clothes. Swann was ordered held without bail.