ROGER PRICE, co-founder of the Price Stern Sloan publishing company, died of respiratory failure Thursday at North Hollywood Hospital. He was 72 . . . A BOMB EXPLODED under a car outside Belfast Friday morning, killing the driver, police said. There was no immediately claim of responsibility, but suspicion fell on militants in the British province's sectarian conflict . . . HYOSUKE NIWA, a former Japanese labor minister, died Friday of heart failure 12 days after he was stabbed by a mental patient, officials said. He was 79. Niwa had been in a coma since he was stabbed, a spokesman said.