NEW YORK, SEPT. 29 -- Republican Rudolph W. Giuliani, badly trailing Democrat David N. Dinkins in the mayoral race here, has decided to run against Jesse L. Jackson instead. In his fiercest attack of the campaign, Giuliani said today that "David Dinkins has associated himself with the philosophy, programs and policies of Jesse Jackson," which "would bankrupt this city." Giuliani challenged the Democratic nominee to "disavow" Jackson's positions on Israel, racial quotas and other issues. Escalating a risky strategy crafted by media consultant Roger Ailes, the former U.S. attorney is attempting to tar Dinkins among Jewish voters for whom Jackson is anathema. Giuliani sparked controversy Thursday with an ad in a Yiddish newspaper that featured a photo of Dinkins with Jackson, the civil rights leader who has twice sought the Democratic presidential nomination. Giuliani's assault drew praise from GOP political consultant Jay Severin. "This is his biggest gun, and he's got to fire it," Severin said of Giuliani's uphill campaign in this racially divided and overwhelmingly Democratic city. "This is the case he has to make to win. I don't think there's anything improper about it." Severin added, however, that "using a Jewish paper as a springboard tactically is a mistake because it looks like pandering." But Dinkins adviser Mark Green said, "It looks like Ailes has found a Willie Horton to try to smear an opponent," referring to the furloughed black, Massachusetts murderer used in ads against 1988 Democratic presidential nominee Michael S. Dukakis. "This is far more likely to hurt Giuliani from a backlash among fair-minded Jewish voters." Dinkins, the Manhattan borough president who has frequently campaigned with Jackson, brushed off the attack, saying candidates should "bring people together rather than divide them." But his spokesman, David Fishlow, accused Giuliani of "a campaign to distort David's positions," saying part of the attack was "so preposterous I'm embarrassed by the need to respond to it." "Clearly, Giuliani is trying to pit black against white," said Teamsters union leader Barry Feinstein, a key Dinkins supporter. "He's trying to turn this into a race war." Speaking to reporters in Manhattan, Giuliani said his references to Jackson had "nothing to do with race." He accused the news media and some Jewish critics of a "double standard" for assailing his tactics while failing to object to Dinkins's labeling him a "Reagan Republican." "I've had to explain over and over again my agreements and disagreements with Ronald Reagan," Giuliani said. "Well, Ronald Reagan wasn't on the platform with me when I won the Republican primary. Jesse Jackson was on the platform with David Dinkins . . . . "David Dinkins and Jesse Jackson have taken the position that part of Israel should be given to the Palestinians . . . . Are we going to have quotas if David Dinkins becomes mayor of this city? Is David Dinkins as mayor going to support a separate homeland in Israel for the Palestinians? . . . Jewish people in this city have a right to ask that question." Giuliani also chided Dinkins for saying that international law should govern whether Palestinian Liberation Organization leader Yasser Arafat can address the United Nations. He questioned whether Dinkins as mayor would "invite" Arafat to New York. "If Giuliani is trying to establish some link between Dinkins and Arafat, he will have to scramble better than that," Fishlow replied. He said Dinkins disagrees with Jackson's Middle East policy and criticized Jackson in 1984 after Jackson referred to New York as "Hymietown." As for quotas, Fishlow said Dinkins "believes in affirmative action" and that "minority people ought to have a leg up when of equal competence." Joe Johnson, director of Jackson's National Rainbow Coalition, said Jackson thinks that Giuliani is "injecting divisive racial overtones into the campaign" and appealing to "the worst fears of people."