WASHINGTON--The nation's major civil rights coalition yesterday stepped up its attack on Chief Justice designate William H. Rehnquist, arguing in a report that he has opposed equal justice for minorities "at every turn."

The Leadership Conference on Civil Rights issued its report a week before scheduled Senate debate on the nominations of Rehnquist and of Antonin Scalia as a Supreme Court associate justice.

While the report covered many of the criticisms leveled at Rehnquist during his confirmation hearings in August, it was characterized by its use of harsh language.

The Leadership Conference, composed of 185 organizations, said its main reason for opposing Rehnquist's nomination "is his 35-year record of opposition to the fundamental principle of equal justice under law."

The coalition also contended "he lacks the requisite candor and sense of propriety to serve in the nation's highest judicial post."

Supreme Court spokesman Toni House said there would be no comment on the study, entitled "The Case Against William Rehnquist: A 35-Year History of Hostility to Victims of Discrimination and Unanswered Questions of Candor and Sense of Propriety."

The report reviewed Rehnquist's career as a private citizen, a Justice Department official during the Nixon Administration and an associate justice on the Supreme Court for the past 15 years.

"He has opposed fair and equal treatment of minorities at every turn: in the legislature (where he opposed local public accommodations laws), at the polls (where he sought to block blacks and Hispanics from voting), and in his personal dealings (where he accepted racial and religious restrictive covenants on his real estate holdings)," the report said.

"As times changed and a consensus for civil rights emerged among the American people, Mr. Rehnquist has sought to put a more benign face on his previous statements and actions. But his explanations are contradicted by others and by common sense," it added.

Much of the study covered Rehnquist's record on issues such as school desegregation, voting rights, public accommodations and racial makeup of juries.

Under a section entitled "Candor and Sense of Propriety," the report cited Rehnquist's failure to disqualify himself from a challenge to the Army's former domestic surveillance program. It said Rehnquist "prejudged the case" and "neglected to acknowledge" his role in formulating the program--a role the justice has denied ever playing.

Reflecting on Rehnquist's early career, the report cited his oft-quoted memorandum while a Supreme Court law clerk in 1952 to Justice Robert Jackson.

The memo defended the 1896 court decision accepting "separate but equal" facilities for Blacks. Rehnquist told the Senate that it represented the views of Jackson, not his own.

However, Jackson's secretary at the time, Elsie Douglas, wrote a senator on August 8 that Rehnquist's recollection was wrong.

A few years after writing the memo, the report said, Rehnquist opposed a Phoenix school desegregation plan and wrote a local newspaper that "we are no more dedicated to an 'integrated' society than we are to a 'segregated' society."

On voting rights, the report recalled Rehnquist's role in a Republican ballot security program in Phoenix in the mid-1960s. Witnesses told the Senate Rehnquist harassed minority Democratic voters, although other witnesses said he did not.

At the time Congress was considering the 1964 Civil Rights Act, the report said, Rehnquist testified against a Phoenix ordinance to desegregate public city accommodations.

Once on the court, the report said, Rehnquist consistently denied requested stays of school desegregation orders approved by lower courts, but he issued an extraordinary last-minute stay that delayed desegregation of Columbus, Ohio, schools for a year.

Rehnquist voted alone for the right of segregated private schools to tax-exempt status, and in the 33 cases where he voted in favor of a race discrimination complainant, 31 were so clear the court was unanimous, the study said. In 14 civil rights cases where he cast the crucial vote, he went against the civil rights litigants, it contended.