Presidential rivals George Bush and Michael Dukakis encountered loud, hostile demonstrators Tuesday as Oregon shipyard workers shouted ``union buster'' at the Republican candidate and anti-abortion activists called the Democratic nominee ``baby killer.'' ``Do not gamble on another liberal Democrat coming out of nowhere,'' Bush said, shouting to be heard over the boos of workers at Northwest Marine Iron Works in Portland, Ore. In the Chicago suburb of Niles, Ill., Dukakis was interrupted for several minutes by the anti-abortion protesters early in a speech on economic policy. ``I just hope as the campaign goes on we can address the real issues that face the campaign and that face the country and do so in a way that's respectful of each other,'' he said afterward.