The Senate opened debate on a major civil rights bill yesterday as White House officials and sponsors of the legislation struggled to break an impasse over key provisions that have prompted threats of a presidential veto.

Despite a day of meetings and telephone conversations with White House Chief of Staff John H. Sununu, who was attending the economic summit in Houston, the two sides remained at odds on key points, Senate Minority Leader Robert J. Dole (R-Kan.) said late yesterday.

The bill would reverse a series of recent Supreme Court rulings that make it harder for workers to sue their employers for job discrimination by limiting the scope and remedies of existing anti-bias laws. It would also allow victims of all forms of intentional discrimination to sue for compensatory and, in extreme cases, punitive damages, which are currently available only in racial discrimination cases.

The Bush administration objects to the damages provision and, in what has emerged as the most serious dispute, contends that reversal of a ruling dealing with standards for proof in discrimination cases would force employers to impose quotas for hiring and promotion to escape costly litigation.

In a letter yesterday to Sen. Edward M. Kennedy (D-Mass.), floor leader for the bill, Sununu suggested what he characterized as a compromise and said agreement on the "quota" issue would pave the way for accommodation on other matters.

But proponents of the disputed provision said Sununu's proposal would not have the effect of fully reversing the court's ruling. "Negotiations are continuing, but so far the administration's proposals have not been satisfactory," Kennedy said last night.

In the opening debate, Kennedy argued that the Supreme Court had made an "abrupt and troubling departure from its historic vigilance in protecting civil rights" at a time when the rest of the world was advancing the cause of democracy and freedom. "The ongoing struggle for justice and opportunity has been significantly undermined by a series of unfortunate decisions by the Supreme Court," he said.

In response, Sen. Orrin G. Hatch (R-Utah) argued that the legislation envisions the kind of curbs on private enterprise that the rest of the world is abandoning. It would lead to a "litigation bonanza for lawyers" and "make it impossible for business people to do business," he said.

Before getting to the bill's key provisions, Senate Rules Committee Chairman Wendell H. Ford (D-Ky.) proposed an amendment extending anti-discrimination laws to employees of the Senate, who are currently protected only by a Senate rule against employment bias.

The key vote to approve Ford's proposal was 74 to 18. A proposal by Iowa senators Charles E. Grassley (R) and Tom Harkin (D) to give Senate employees the right to sue was rejected 63 to 26.

Ford's proposal was aimed largely at resolving a separate dispute over the legal rights of Senate employees to sue individual senators under a pending bill to extend civil rights protections to the disabled. By bringing Senate employees under the protection of all anti-discrimination laws, Senate leaders hoped to hasten final approval of a House-Senate compromise on the disabilities legislation.

But critics contended that the move would make it too easy for senators to escape lawsuits that other employers would face under the new civil rights bill.