The Senate narrowly sustained President Bush's veto of the 1990 Civil Rights Act yesterday, dooming the measure for this year and sharpening the political debate over race and sex discrimination just two weeks before the Nov. 6 elections.

With white supremacist David Duke watching from one section of the gallery and black civil rights leader Jesse L. Jackson observing briefly from the other side of the chamber, the Senate voted 66 to 34 to override Bush's veto, falling one vote short of the 67 needed to enact the bill over the president's objections.

Bush vetoed the legislation Monday after months of argument between administration officials and the bill's backers over whether it would force employers to use hiring and promotion quotas to fend off costly litigation.

In yesterday's vote, the bill's backers picked up one more vote when Sen. Rudy Boschwitz (R-Minn.), who is in an increasingly close race for reelection this fall, switched sides after it was clear that the veto would be sustained. Boschwitz, who had voted against passage of the legislation, voted yesterday to override the veto.

As in previous votes on the legislation, all 55 Senate Democrats, including conservative southerners, voted for the bill. They were joined by 11 Republicans: John H. Chafee (R.I.), William S. Cohen (Maine), John C. Danforth (Mo.), Pete V. Domenici (N.M.), Dave Durenberger (Minn.), Mark O. Hatfield (Ore.), John Heinz (Pa.), James M. Jeffords (Vt.), Bob Packwood (Ore.), Arlen Specter (Pa.) and Boschwitz. Among Washington area lawmakers, only John W. Warner (R-Va.) voted to sustain the veto.

The legislation, cosponsored by Sen. Edward M. Kennedy (D-Mass.) and Jeffords, would have reversed or modified six recent Supreme Court rulings that made it more difficult for women and members of minority groups to win job discrimination suits. It would also have expanded monetary remedies available to victims of job discrimination now ineligible to receive such damages.

A key provision of the bill would have overturned Wards Cove Packing Co. v. Atonio, which effectively set aside an 18-year-old standard putting the burden of proof on businesses to show that hiring and promotion practices that have a disproportionate negative impact on women and minorities were based on business necessity, not discrimination. Wards Cove shifted the burden of proof to workers.

The bill would have shifted the burden back to employers under terms of legal art that became the principal focus of the debate between the bill's proponents and the White House, which contended that employers could defend themselves from legal attack only by resorting to quotas.

In a final bid for votes to sustain the veto, Minority Leader Robert J. Dole (R-Kan.) said the Senate could still win enactment of a civil rights bill this year by approving an alternative drafted by Bush that has been rejected by the bill's sponsors and civil rights groups as worse than no bill at all.

An earlier proposal from the administration was "nothing short of outrageous," said Republican Jeffords, and the new proposal is a "step backward" from that.

Spurning Dole's proposal for passage of the Bush alternative, Kennedy said efforts to pass civil rights legislation this year were over but promised to return next year, possibly with a stronger bill, and said he was confident of winning.

In an unusually scathing criticism of Bush, Kennedy accused the president of resurrecting the "Willie Horton strategy" of his 1988 campaign, a reference to the Massachusetts convict whose furlough became an issue in the campaign. "It is bad enough to resort to such disgraceful tactics in a political campaign," said Kennedy. "But it is far more serious when a president of the United States, who is supposed to be president of all the people, dishonors his high office, abuses the noble cause of civil rights and stoops to divisive appeals to prejudice and resentment."

Leading the fight to sustain the veto, Sen. Orrin G. Hatch (R-Utah) argued that the bill would spark "tension and discord in the workplace," promising "preferential treatment on the basis of race, ethnicity, color, religion and gender for some Americans."