Thirty-odd years ago, Eric Sevareid of CBS recorded an interview with Justice Hugo Black. Today, in the week that David Souter succeeds William Brennan on the U.S. Supreme Court, one telling moment of that interview may usefully be recalled.

Only a few years before the interview, the court had decided Brown v. Board of Education. In that landmark case, a unanimous court put an end to state laws enforcing racial segregation.Sevareid gently needled his subject. After all, he noted, 60 years had elapsed between the Plessy case of 1896, upholding the rule of "separate but equal," and the Brown case of 1954, in which the rule was summarily abandoned. In this period, Sevareid remarked, the Constitution had not changed by a relevant comma. How could the meaning of the Constitution have changed so dramatically?

Black tented his fingers and smiled. In the soft accents of Ashland, Ala., he replied: "That's right, Mr. Sevareid," he said, "that's right. The Constitution hadn't changed - but the judges had changed."

When Souter takes his seat, unless all the commentators are greatly mistaken, we will embark upon a period in which the Constitution significantly changes.

The key words of the Constitution will not have changed. But the composition of the court will have changed. Souter went out of his way during his confirmation hearings to lavish praise upon the departed Brennan. This was lapidary stuff, not to be taken seriously. Brennan and Souter look at the Constitution from opposite poles.

Over the past 10 years at least, Brennan brilliantly led the liberal wing. The warmth of his personality combined with the sharpness of his mind. Brennan's gift was to charm the birds out of the trees. He could count on Justices Marshall and Blackmun almost all of the time; he could win Stevens' vote most of the time. In six of the 37 cases that were decided 5-4 in the 1989 term, Brennan picked up the vote of Justice White to put together a winning coalition.

With his resignation, Brennan leaves a vacuum behind. The laws of physics do not apply. Nothing is going to fill the vacuum. Marshall is 82, a burned-out volcano. Blackmun will be 82 in November; he was born to follow, not to lead. Stevens, at 70, has none of Brennan's easy manner. The liberal wing barely flutters.

This will become clear as the term moves along. Most casual observers of the high court see only the formal, written opinions. There were 129 of these in the past term. The unseen often counts for as much as the seen. Under the court's traditional procedure, an appeal will not be accepted unless at least four justices vote to put it on the docket. Four affirmative votes are often hard to come by. In the past week, the court granted only 27 petitions for review - 27 out of 1,200 that were pending.

With Brennan no longer voting for review of touchy cases, a number of sensitive issues may not be taken up at all. Lower court decisions will be left in force.

On other questions, dear to the conservative heart, Souter may cast a fourth vote to hear the cases argued. The shaping of the Constitution begins behind the locked doors of a Friday conference. Here the court sets its agenda and the chief justice assigns the writing of majority opinions.

One other truism should be kept in mind. Historically, justices have refused to be tied. They will not be tied to ideology or to the presidents who chose them. Given life tenure, they are responsible to no one.

Tides ebb and tides flow. Over a period of 35 years, extending roughly from 1935 through 1970, liberals could look forward to a term of court in a sense of pleasant anticipation. Their justices set the agenda. Earl Warren and Bill Brennan wrote the key opinions. They effectively changed the Constitution. With Souter aboard, it's the conservatives' turn.