Voters' doubts about George Bush and Michael Dukakis are such that, despite Bush's recent strength in the presidential race, the debates between the two men will prove critical, analysts of a new poll suggested Thursday. ``We consider this contest still a very close one,'' said Andrew Kohut, president of the Gallup Organization, which conducted the poll for the Times Mirror Corp. The poll suggested that Bush has gained in the presidential race more by solidifying his support among Republicans and Republican-leaning independents than by siphoning off Democrats from Dukakis. ``He has performed in a way that has caused Republicans to come home,'' analyst Norman Ornstein said at a news conference where the poll results were released. Kohut said Bush ``has won the first round of this campaign and seized the momentum,'' but that support for both men was ``soft,'' with many people who expressed a preference saying they might switch to the opponent. Ornstein, of the American Enterprise Institute, said Bush was vulnerable on the Iran-Contra affair and on the administration's handling of drug charges against Panamanian leader Manuel Antonio Noriega, with the Noriega question ``more significant to people'' than any other issue. Bush's criticism of Dukakis' prison furlough program ``resounds with more voters than any other charges'' against the Massachusetts governor, Ornstein said. Voters are also sensitive to Dukakis' veto of a bill that would have required the Pledge of Allegiance in Massachusetts schools, not because it raises questions about Dukakis' patriotism, but because the public thinks his judgment was wrong, Kohut said. The poll analysis called Bush's running mate, Sen. Dan Quayle of Indiana, ``the achilles heel of the Republicans'' because of doubts about his qualifications. While Quayle did not appear to be an issue on which votes were swinging directly, Ornstein said Quayle would be ``more of an issue than the overall numbers suggest'' as ``a symbol of George Bush's judgment combined with Noriega and Iran-Contra.'' ``Given the doubts ... whether either candidate has the judgment to be a good president ... these debates are either going to reinforce doubts or erase doubts about their judgment,'' Ornstein said. ``I think the debates are critical.'' Bush and Dukakis have their first debate Sunday in Winston-Salem, N.C., their second on Oct. 13 or 14 in Los Angeles. The poll suggested that Bush has advanced his cause by painting Dukakis as ideologically out of step, and he has benefited from increased voter satisfaction with the nation's course and confidence in the economy. But while Bush has drawn some conservative Democrats to his side, he has lost ground among other Democratic-oriented groups, said Gallup's analysis. It said the more significant movement was Bush's greater support from Republicans in general, and particularly from Republican-leaning, blue-collar conservatives identified in the survey as ``disaffected'' voters. ``For all the talk of the importance of the Reagan Democrats, this analysis suggests that the most significant dynamic in recent weeks has been the return of Republicans to the fold _ with disaffecteds showing the largest proportionate swing,'' Gallup's analysis said. The ``disaffecteds,'' set apart by their suspicion of government, made up about a tenth of the registered voters in the poll. They went from a nearly even division on Bush and Dukakis in May to backing Bush by 61 percent to 27 percent this month, Gallup said. The poll defines the electorate by grouping voters with shared values, rather than through the more traditional measures of political party identification or ideology. Bush has made inroads only in the most conservative Democratic groups, Kohut said, and he lost ground among another Democratic group, ``seculars,'' who are non-religious and put an emphasis on personal freedom. A pro-Dukakis group, the liberal ``'60s Democrats,'' supports Dukakis more strongly now, apparently in reaction to Bush's ideologically based attacks. At the same time, core Republican groups support Bush almost unanimously, and in each ``there has been a dramatic increase in the proportion who say they support Bush strongly,'' Gallup's analysis said. As a result, it said, ``It is clear that the main effect of the Bush efforts has been to solidify his base among Republican-oriented groups.'' Overall, Bush was supported by 50 percent in the poll of 2,001 registered voters to 44 percent for Dukakis. The survey, done Sept. 9-14, had a margin of error of three percentage points, so Bush's lead was not statistically meaningful. But, in this as in other polls, Bush had trailed badly before the Republican convention in August.