Democratic presidential nominee Michael Dukakis begins his race against Republican George Bush with a 12-point advantage, according to an ABC News poll. The network reported Thursday that Dukakis leaped to a 53-41 percent lead in a survey of 450 registered voters Wednesday, up from his 45-46 virtual dead heat with Bush in ABC's poll Sunday. The movement was 13 points _ from 1 point down to 12 up. The jump was expected; polls in other elections have found that nominees often gain support immediately after their party's convention. Such bumps frequently settle back down as voters focus on the substance of the race. The survey reflected the success of Dukakis' peacemaking with Jesse Jackson, his opponent for the nomination. Sixty-eight percent said Dukakis was treating Jackson fairly, up from 52 percent in a poll early this month. Similarly, 70 percent said Jackson was treating Dukakis fairly, and the share of respondents with an unfavorable view of Jackson fell 11 points from Sunday, to 31 percent. Those with a favorable view rose 9 points to 52. The national survey found a rise in unfavorable views of Bush, who was roundly criticized by convention speakers this week. His favorable rating fell from 49 percent to 41 percent, while those viewing him unfavorably rose from 36 percent Sunday to 44 percent Wednesday. The poll, completed the day before Dukakis appeared at the convention, found little change in his favorable-unfavorable rating, 55-21. Dukakis' 12-point lead against Bush did not mark his greatest numerical advantage in an ABC poll; the Massachusetts governor led by 53-40 in late May. The margin of error for the new poll was 5 points. Such single-day surveys, particularly when conducted during or just after a highly publicized event, tend to measure visceral reactions rther than considered opinion, so the views they gauge can change rapidly. Dukakis continued to do better with women voters than with men, and the poll Wednesday found that he had gained more ground among women _ leading Bush by 25 points in the new poll, up from an 8-point lead Sunday. Dukakis scored a tie with Bush among men, after a 12-point Bush lead Sunday. Dukakis improved with independents, scoring 48-42 against Bush after a 52-35 lead for Bush among independents Sunday. And 59 percent of Democrats who had bolted the party to vote for President Reagan favored Dukakis now. In another measure of the convention's impact, 52 percent said the Democrats could be trusted to do a better job with the nation's problems, up 9 points from Sunday. And 40 percent said they generally approved of the proceedings in Atlanta, while just 13 percent disapproved. Nearly half said they had not been paying enough attention to say.