True believers on both sides share an enviably clear view of the shape that the Supreme Court will take if U.S. Appeals Court Judge Robert H. Bork survives the Senate confirmation process.

As expressed by Daniel J. Popeo, founder of the conservative Washington Legal Foundation, "We have the opportunity now to roll back 30 years of social and political activism by the Supreme Court." Making the same point from a different perspective, Ralph Neas, executive director of the Leadership Conference on Civil Rights, said Bork's confirmation would "jeopardize the civil rights achievements of the past 30 years."

Perhaps. Those of us in the hold-the-coats fraternity on the journalistic sidelines like a fight, which may account for our largely uncritical acceptance of the suggestion that the fate of western civilization hangs on Bork's confirmation. Some of us once were equally certain that the appointment of Warren E. Burger as chief justice, or of William H. Rehnquist after him, would radically change the balance of the court.

But history suggests that picking Supreme Court justices is less than an exact science. Times change and justices change. Many disappoint those who appointed them.

The late Justice Hugo F. Black, arguably the court's greatest civil libertarian, was a highly partisan Democratic senator from Alabama, one of the few to support President Franklin D. Roosevelt's plan to enlarge the court and pack it with justices who supported the New Deal.

After the Senate had rejected the court-packing proposal, an angry Roosevelt put Black on the court in 1937. It was not revealed until later that Black had belonged to the Ku Klux Klan, a disclosure that caused an enormous uproar and demands for his resignation.

Instead of retiring, Black served with distinction for 34 years. He called himself a strict constructionist, saying, "Judges take an oath to support the Constitution as it is, not as they think it should be." Today's conservatives would cheer that statement, but many of them would be less enthusiastic about Black's strict defense of the First Amendment, which he said prohibited restrictions on freedom of speech "without deviation, without exception, without any ifs, buts or whereases . . . ."

Earl Warren began his career as a tough-minded prosecutor in Oakland, Calif., advancing to become attorney general and then governor of California. President Dwight D. Eisenhower named him chief justice in 1953.

Despite Warren's law-enforcement credentials, conservatives viewed him as a national symbol of judicial permissiveness after his 1966 Miranda decision requiring that criminal suspects be advised of their rights. Many thought the 5-to-4 Miranda decision would not survive Warren's departure from the court, but his successors have only chipped away at the edges. Police have learned to live with the ruling, and the jails are full.

President Reagan knows something about judges who fail to meet the expectations of those who appoint them. Donald Wright, named by then-Gov. Reagan to head the California Supreme Court, struck down the state's capital punishment statute. Reagan intimates were outraged, saying that Wright had favored the death penalty before his appointment. Wright denied making any commitment, while others said that he had merely changed his mind.

Justices do change their minds. Sometimes they also are overcome by common sense, as Justice Sandra Day O'Connor may have been recently when she dissented from an opinion by Justice Antonin Scalia that prevented a former Army sergeant who had been given LSD without consent from suing the government.

Scalia held that preservation of military discipline required broad immunity from lawsuits. His fellow Reagan appointee O'Connor agreed that immunity was important but wrote that "conduct of the type alleged in this case is so far beyond the bounds of human decency" that "it simply cannot be considered a part of military discipline."

Whether Bork will be confirmed by the Senate is not clear. What is even less clear is whether the court would be transformed by his presence. Perhaps the true believers will once again be disappointed.

Reaganism of the Week: Speaking to conservative political activists last Wednesday, the president said, "I've always thought that the common sense and the wisdom of government were summed up in a sign they have hanging on that gigantic Hoover Dam. It said, 'Government property. Do not remove.' "