Exxon said that more than 500,000 gallons of heating oil--not 5,000 gallons--may have leaked from its underwater pipeline into the Arthur Kill shipping channel at Linden, N. J. Coast Guard spokesman Jeff Crawley said the company put the size of the spill at between 420,000 gallons and 546,000 gallons. The Coast Guard at first estimated the leakage of No. 2 oil, discovered Tuesday morning, at 5,000 gallons. Meanwhile, emergency crews worked to contain the floating oil with booms and traps and were vacuuming the surface of the channel, which separates New Jersey from Staten Island, N.Y. Divers found a gash 4 feet long in the pipeline.