Charles J. Cooper, a top deputy to Assistant Attorney General William Bradford Reynolds, was sharply questioned about the administration's civil rights policies yesterday at a Senate hearing on his nomination to be the Justice Department's top legal adviser.

With one exception, however, Cooper avoided the questions about credibility that helped lead the Senate Judiciary Committee last June to reject Reynolds' nomination to the department's No. 3 post.

The soft-spoken Cooper, 33, who has been nominated to head the department's Office of Legal Policy, responded to questions cautiously and largely avoided the acrimony that characterized Reynolds' confirmation hearings.

Civil rights activists, who strongly oppose the conservative Cooper, declined to testify yesterday, saying Cooper's role at the department's Civil Rights Division was less clear than Reynolds'. And the two Republican senators who voted against Reynolds, Arlen Specter (Pa.) and Charles McC. Mathias Jr. (Md.), played no role.

Cooper is a former law clerk to Supreme Court Justice William H. Rehnquist. The only opposition witness at his hearing was Birmingham Mayor Richard Arrington, who charged Cooper with "actively misrepresenting facts and allegations before a court of law" in an affirmative action case.

Despite a four-year-old consent decree -- approved by the Justice Department -- that allows Birmingham to hire minorities and women for city jobs over more qualified whites, the department has reentered the case on the side of white employes charging reverse discrimination. Cooper contends that the city is misinterpreting the agreement, but a deposition by the department lawyer who negotiated the decree supports the city's version.

Sen. Joseph R. Biden Jr. (D-Del.) cited a memo in which Cooper said an antibusing bill was unconstitutional but that an argument could be devised to support it. Cooper said he had given the issue only cursory review.

"It's your mindset that bothers me," Biden said. " . . . I've just got a feeling you all are sitting there late at night, with your glasses on and your green eyeshades, saying, 'How can we screw up the Constitution?' "