Assistant Attorney General Charles J. Cooper is a cautious man. Some would say excessively cautious. He doesn't quarrel with the description.

At a recent news conference to release an administration report on federalism, Cooper steadfastly resisted reporters' efforts to get him to say anything remotely newsworthy. He bobbed and weaved with such finesse that some of the assembled journalists were left wondering why the news conference was held at all.

Peppered with questions about the report's thesis, that the federal government and the Supreme Court have usurped too much power from the states, Cooper said: "That's a difficult question to answer on a yes-or-no basis . . . . I can't say from the standpoint of having exhaustively researched the issue . . . . Each of these ideas would have to be examined in a coordinated fashion . . . . This report does not seek to undo anything."

Cooper's meticulously careful demeanor belies an aggressive brand of conservatism that has embroiled him in controversy since he became the Justice Department's chief legal adviser a year ago. A former law clerk to Chief Justice William H. Rehnquist, Cooper, 34, now runs the Office of Legal Counsel, which Rehnquist headed during the Nixon administration.

Cooper's understated approach should not be mistaken for a lack of political savvy. He was part of a small White House-Justice "team" that guided Rehnquist through his grueling Senate confirmation hearings last summer. When the White House rejected a Senate request for Rehnquist's papers from the Office of Legal Counsel, Cooper strongly defended the claim of executive privilege before it was dropped.

The fervor he arouses in others far outstrips the tenor of his own public comments.

"Chuck Cooper has been the point man for the radical right in the Department of Justice," said Ralph G. Neas, executive director of the Leadership Conference on Civil Rights. "He's the driving ideological force there. We've always viewed him as a captain of the group that has embarrassed the administration on civil rights and other issues."

While such accusations swirl around him, Cooper sticks to his scholarly style, sprinkling his conversation with such phrases and words as "doctrinal developments" and "litigable."

"I have to confess I value precision in communication," the soft-spoken southerner said in an interview. "I'm not unacquainted with occasions on which I think things did get distorted."

While serving in effect as lawyer for Attorney General Edwin Meese III, Cooper also advises the Justice Department, other federal agencies and inquiring members of Congress on a wide range of legal questions. Most of his opinions remain confidential, but some that have surfaced have generated headlines.

In one opinion, Cooper argued that employers may fire persons with AIDS because of fear that the disease may be contagious, even if that fear is irrational. In another, he said that President Reagan must support an executive privilege claim by former president Richard M. Nixon to keep Nixon's White House papers secret.

In a third argument, this one upheld by the Supreme Court, Cooper said the Gramm-Rudman-Hollings budget-balancing act was unconstitutional because it allowed an arm of Congress, the General Accounting Office, to infringe on executive branch policy-making.

In addition, department sources say, Cooper has been advising Meese on the U.S. decision to allow arms to be shipped to Iran in connection with efforts to free American hostages. Meese, in turn, has provided assurances to the White House that the shipments were legal.

Cooper's philosophical outlook was molded in part by his 1978 clerkship with Rehnquist. Cooper had just graduated from the University of Alabama Law School and briefly practiced law in Atlanta. He still speaks reverently of working for "The Boss," as Rehnquist's clerks call him.

"It was the highlight of my career thus far," Cooper said. "Two years out of law school, discussing legal issues with a Supreme Court justice -- it's so heady it's numbing . . . . Part of the reason I wanted this job was because he had it. He spoke fondly of his time here."

Cooper reserves his strongest language for the Senate battle over Rehnquist's ascension to chief justice. "The challenge made to his integrity was something I think was unfortunate," he said. "That did leave me with a real bad taste in my mouth."

Rehnquist is not Cooper's only prominent predecessor. Supreme Court Justice Antonin Scalia held the job during the Ford administration. Theodore B. Olson, who ran the office in President Reagan's first term, is now under investigation by an independent counsel for possible perjury in connection with an executive privilege dispute over Environmental Protection Agency documents.

The work of Cooper's 18-lawyer office ranges from the fascinating to the obscure. "We get some of the neatest questions in this office, and we get them before anyone else, like Gramm-Rudman," he said. "The issues we get range from the biggest and most interesting constitutional issues to questions like who has jurisdiction over coyote control in western states."

The root of Cooper's caution is not hard to find. In 1982, four months after becoming a deputy to Assistant Attorney General William Bradford Reynolds, Cooper found himself in the midst of a torrent of criticism over the Bob Jones University case.

Cooper concedes that the administration's move to allow tax breaks for private schools that discriminate against blacks was a political disaster. But he continues to argue that people misinterpreted its real position, that the Internal Revenue Service had exceeded its authority in revoking the tax breaks and that legislation was needed to accomplish that end.

Still, Cooper said, "I got a taste for what can happen if you proceed without measuring and calculating your steps with the public and the press in mind."

Cooper got a similar taste after his recent legal opinion that employers can discharge victims of acquired immune deficiency syndrome because of contagion fears without violating discrimination laws. Rep. Henry A. Waxman (D-Calif.) called the opinion "tortured." New York attorney Harry N. Turk said Cooper took "some unusual legal twists and turns to come up with that conclusion. Every medical expert I've ever heard says it cannot be transmitted casually in the workplace, so how can that be a basis for discrimination?"

"I've heard all the arguments against our analysis," Cooper maintained, "but to me they're not as faithful an interpretation of this statute. I don't think we could have called it differently."

Cooper acknowledged that his legal reasoning could allow employers to discriminate against AIDS victims by relying on a pretext. But, he said, "Those people who are intent on doing that are going to do it. They're going to find another way."

In the Nixon papers case, Cooper's opinion said an incumbent president is almost always bound by a former president's claim of executive privilege. In keeping with his sweeping view of presidential power, Cooper also said that other top officials have no choice but to go along.

Rep. Glenn English (D-Okla.) called the opinion "flawed" and "legally deficient." He criticized Cooper for saying the courts would resolve the dispute in any case, calling this "very strange legal advice to give. It's like telling your client, 'Don't worry about it. I've done a bad job and made matters more complicated, but we're going to get sued anyway.' "

Cooper also drew flak over the administration's task force on federalism, which said the Reagan administration has tried to reverse the longtime infringement on states' rights by federal authorities. Cooper appeared unfazed by criticism that Reagan has also infringed on the states when it was convenient.

"There is no principle that can't, on occasion, be overwhelmed by principles that are simply more important," he explained.

As Rehnquist was in an earlier era, when he churned out advice on school segregation, the Equal Rights Amendment and surveillance of antiwar protestors, Chuck Cooper is the administration's legal strategist on the most sensitive issues of the day. But Cooper doesn't view his role as telling his political clients what they want to hear.

"The description of this office as just providing a legal justification for anything that is done is inaccurate," he said. "In some quarters, we're known as 'Dr. No.' "

BACKGROUND:

Assistant attorney general in charge of the Office of Legal Counsel; age 34. Undergraduate and law degrees from the University of Alabama; worked two years at an Atlanta law firm. Clerk for Supreme Court Justice William H. Rehnquist. Deputy assistant attorney general in the Civil Rights Division from 1981 to last November.