THE SUPREME COURT: How It Was, How It Is <i> by William H. Rehnquist (Morrow: $19.95; 325 pp.)</i>

The aura of power of the U.S. Supreme Court may have much to do with the mystery that surrounds it. Nine black-robed justices go behind closed doors to decide some of the most vital public questions of the day. No TV cameras, no reporters, not even aides or clerks to record the deliberations.

Justice Louis Brandeis once observed that the court is respected because “we do our own work.” And unlike so much of official Washington, they do it hidden from public view.

The nation’s 16th chief justice, William H. Rehnquist, is very much a creature of the court. Stiff and gawky in public, Rehnquist can be charming, humorous and self-effacing in private. He even jokes about his reputation as a foe of civil rights and liberties. He took the podium at a recent court reception on the anniversary of the introduction of the Bill of Rights. “I want you to know,” Rehnquist deadpanned, “that I favored June 25th, the anniversary of the enactment of the Alien and Sedition Acts.”

Though he is very much the legal scholar and judge, it is hard to imagine Rehnquist being elected to any political position. He appears painfully shy and awkward before groups or in front of a camera. His indelible public image may have been formed at last year’s Senate hearings on his confirmation. Called a right-wing extremist, he sat stiffly and said as little as possible. He looked like a defendant on trial.

Rehnquist has now written a book that tries to dispel some of the mystery about the court and about him. Born and reared in a Milwaukee suburb, Rehnquist went out West, to Stanford, where he graduated first in his law class. And as it happens, Supreme Court Justice Robert Jackson journeyed out in 1951 to dedicate a new law building and interviewed young Rehnquist for a clerkship. To his surprise, Rehnquist got a letter offering him the job. He bought a 1941 Studebaker and drove U.S. 40 across America to Washington.

He portrays himself as the Western provincial freshly arrived in the big city. Invited to a dinner party with other clerks at the Georgetown home of Justice Felix Frankfurter, he encounters vichyssoise.

“I came within a hair of calling the maid’s attention to the fact that my soup was cold and ought to be reheated,” he reports.

Only a few months before Rehnquist arrived, President Harry S. Truman, fearing a threat to the Korean War effort, ordered troops to seize the steel mills and keep them running. The companies filed suit, and the case quickly came before the Supreme Court. All nine justices had been appointed by Truman or his predecessor, Franklin D. Roosevelt. Yet, on June 2, 1952, the court rebuked the President on a 6-3 vote.

Why did the court call a halt to years of steadily expanding presidential power? Rehnquist points to public opinion. The Truman Administration was coming to an unhappy end. Stuck in a stalemated war in Korea and beset by a slew of scandals, Truman overplayed his hand in the steel case and got slapped down for it.

Supreme Court justices, then and now, “read newspapers and magazines, we watch news on television, we talk to our friends about current events,” Rehnquist writes. “No judge worthy of his salt would ever cast his vote in a particular case simply because he thought the majority of the public wanted him to vote that way, but that is quite a different thing from saying that no judge is ever influenced by the great tides of public opinion that run in a country such as ours.”

But that is the most recent case that gets a lengthy analysis. Most of this book is devoted to a history of the court before 1952--in other words, before Rehnquist’s arrival from law school. And a fine account it is. Rehnquist shows how the evolution of the nation shapes the issues before the court. For example, the growth of the railroads after 1865 not only changed the nation but also reshaped its laws.

You will not find here an explanation of the views of the chief justice on controversial issues. Only rarely does Rehnquist the conservative jurist slip through. “The Supreme Court has no generalized mandate to ‘do justice,’ ” he says, commenting on a late 19th-Century case. “It is simply required to decide whether lawsuits dependent on state laws raise any federal constitutional question. Save as restricted by the U.S. Constitution, the states are themselves sovereign entities with their own systems of laws and courts.” His more liberal counterparts on today’s court are not quite so deferential to the states.

In the last two chapters, he gives a guided tour of the court and an explanation of its workings. The workload is enormous: more than 5,000 appeals per year and about 160 cases that are fully briefed and decided with a written opinion.

In a typical work week, a justice must consider which among more than 100 appeals should be heard by the full court, prepare for arguments in 12 cases that will be heard, sit through an hour of debate on each, discuss and vote in conference on those 12 cases and write opinions or dissents in already decided cases.

Two images stand out. After reading the briefs and the lower court opinions, Rehnquist likes to discuss a pending case while walking the halls or the neighborhood with a clerk. “I began to realize,” he says of his first years on the court, “that some of my best insights came not during my enforced thinking periods in my chambers, but while I was shaving in the morning, driving to work or just walking from one place to another.”

On Thursdays, the justices gather around their long conference table, Rehnquist at one end and the court’s 81-year-old liberal leader, William J. Brennan Jr., at the other end. The two are also at the opposite ends of the philosophical spectrum.

First, Rehnquist states his view of the case and announces his vote. Typically, he takes the most conservative view, siding often with the government. Then, it is Brennan’s turn, and he usually sides with the individual or the underdog.

One by one then, in order of seniority, the other justices announce whether they go along with Rehnquist or Brennan. The votes are tallied and the opinion assigned to one justice. Weeks or perhaps several months later, we learn the outcome.

For a nation that so values open political agreements openly arrived at, the Supreme Court is an odd institution but one that serves the nation. It is detached, but not too detached from the political moods. It can be independent and prickly and is often unpredictable. Rehnquist has lifted the veil slightly, but the essential mystery remains.