An estimated 300 demonstrators opposed to a proposed toxic-waste incinerator blocked the gates to what would be the largest facility of its kind in the nation.Police dispatcher Robert Greathouse said no arrests were reported. The protest began Sunday afternoon. Far fewer than the 2,000 people organizers had anticipated turned out for the demonstration against the proposed $140 million incinerator being built by Waste Technology Industries, a subsidiary of Swiss manufacturer Von Roll, on the Ohio River just across from West Virginia. The Rev. John Cheetham, pastor of the First Presbyterian Church in Chester, W.Va., says he fears pollutants from the burner will be trapped in the valley during the area's frequent air inversions. He also is concerned that the site of incinerator is only 400 feet from an elementary school. "We're pretty proud of our technology, as professional environmentalists," Blake Marshall, president of Von Roll of America, said. "It's the most advanced plant of its kind. The possibility of a release or a spill is virtually impossible." Opponents have called for a five-year moratorium on construction of new or expanded incinerators and an outright halt to burning hazardous waste in cement kilns. A citizens' group asked Ohio Gov. George Voinovich last month to halt the project. He refused. But Mr. Voinovich said the state would offer health screenings to residents in the vicinity - both immediately and later on - to measure for any impact from emissions.