Last April, a few weeks after Sen. Edward M. Kennedy (D-Mass.) introduced what would become known as the Civil Rights Act of 1990, Attorney General Dick Thornburgh sent him a letter stating the administration's opposition to six key provisions of the bill.

Seven months and hundreds of hours of negotiating later, Thornburgh could have sent almost the same letter. Although each side made some compromises -- the bill's proponents rewrote at least four significant sections, the administration changed its mind on two basic provisions -- neither gave enough to bridge the gaps between them.

The biggest sticking point remained the same through more than a dozen meetings between administration officials and the bill's proponents that culminated Tuesday with President Bush's veto: Wards Cove v. Atonio, decided by the U.S. Supreme Court last year.

The bill's supporters are determined to nullify the decision, which they say reversed a 19-year-old Supreme Court precedent on "unintentional discrimination." Bush's aides are willing to nullify part of the decision, but they like much of the Wards Cove ruling.

On Capitol Hill yesterday, the bill's proponents scrambled to pick up the two Senate votes and 12 House votes needed to muster the two-thirds margin necessary to override the veto. In the Senate, which will vote first, sources gave the bill's proponents a slim chance of finding the necessary support. "Those last two votes are going to be awfully hard to find," said an aide to one of the bill's supporters.

Kennedy, chief Senate sponsor of the measure, said last night that it is still possible to pull together enough votes to override the veto.

Perhaps the biggest unresolved difference over Wards Cove centers on the question of when a practice that is not discriminatory on its face but which has the effect of shutting out women or minorities can be justified by "business necessity." Both sides said they wanted to protect minorities from subtle forms of discrimination while allowing employers to build the most qualified work forces, but they could not agree how to do it.

In such "unintentional discrimination" cases, workers typically use statistics to show an imbalance in an employer's work force, then attempt to prove that a hiring or promotion practice or system works to exclude women or minorities. Workers have successfully sued over such requirements as intelligence tests and high school diplomas for certain jobs, physical tests for firefighters and subjectively scored oral exams for promotions of bank regulators.

Under the bill passed by Congress, an employer can defend a challenged practice on the basis that it bears "a significant relationship to successful performance of the job." Under an alternative proposed by the White House, an employer could defend a practice on the broader basis that it bears "a significant relationship to a significant business objective."

Justice Department officials suggest that, under the bill's language, an employer might be hard put to defend promoting only workers with outstanding job ratings and that a university might have trouble requiring its professors to have doctorates.

The bill's proponents contend that the legislation would not present any threat to such employment practices, because in both cases the requirement is aimed at how an employee performs on the job.

The White House did change its position on one key issue stemming from Wards Cove that involved who has the burden of proof in a discrimination case. The administration now agrees with the bill's proponents that it is up to an employer to prove that an employment practice meets the "business necessity" standard, not up to the employee to show that it does not.

In addition, the administration agreed with the bill's proponents on the need to reverse another Supreme Court ruling involving intentional discrimination. Both sides now want an employer to be held liable for a discriminatory motive, even if the employer could show an action resulting from such a motive had an otherwise justifiable rationale.

Yet overshadowing these compromises were other issues on which the two sides could not agree:

How specific must an employee be in alleging unintentional discrimination? The bill's proponents gave some ground, but the bill enables an employee to be able to challenge "a group of practices" if the employee cannot, on the basis of the employer's records, identify one specific practice that produces the statistical imbalance. John Dunne, head of Justice Department's civil rights division, said yesterday the bill's language puts an unfair burden on the employer to help prove the employee's argument.

How much can a victim of intentional discrimination recover in damages? The bill's proponents originally said the potential damages should be open-ended, then agreed to limit punitive damages to $150,000 or the amount of compensatory damages plus lost pay, whichever is greater. The administration wants to cap any payments for damages at $150,000.

Under current law, only racial minorities can recover damages in cases of intentional discrimination; women can only receive back pay and a court order reversing a job action such as a firing or the denial of a promotion.

When can court-ordered affirmative action plans be challenged? The bill's supporters want to reverse the Supreme Court's 1989 decision in Martin v. Wilks that allowed greater opportunity for after-the-fact challenges of such orders. The administration claims the bill would deny some individuals their rightful day in court.

At two or three points in the negotiations, both sides appeared hopeful of an agreement. Kerry Scanlon, an attorney with the NAACP Legal Defense and Educational Fund and one of the negotiators for the bill's supporters, said yesterday the hope proved false because the administation "didn't really want a civil rights bill" -- only enough talks to create the appearance that they desired a bill, he said.

Dunne yesterday said the administration negotiated sincerely, saying: "If there was not good faith, the administration would not have invested all that time."

With a Senate vote scheduled this morning, civil rights advocates, labor groups and women's rights organizations focused yesterday on winning the support of five or more Republicans who voted against the legislation with some misgivings.

Sources said the possible swing votes include Sens. Alfonse M. D'Amato (N.Y.), John McCain (Ariz.), Warren B. Rudman (N.H.), John W. Warner (Va.) and Pete Wilson (Calif.). Civil rights groups unsuccessfully pressed these senators to switch their votes last week when the bill was passed. All the Senate Democrats and 10 Republicans supported it at the time.

The difficulties faced by civil rights advocates are compounded by the fact that the president normally gains rather than loses votes among members of his own party on a veto override attempt.

Acknowledging that many Republicans previously voted against the bill out of loyalty to Bush, civil rights leaders tried to recast the override vote as a demonstration of support for working Americans. If the Senate does not vote to override the veto, the House can take no action, and the veto is sustained.

"The deliberate use of the emotionally charged characterization of this bill as a 'quota bill' would seem to indicate that the President is trying to make a political point, not a legal or legislative point," said Jesse L. Jackson in a statement.

Staff writer Helen Dewar contributed to this report.