The internal politics of the Supreme Court under Chief Justice-designate William H. Rehnquist may undergo a significant and immediate change, pulling to the right the moderate center that has been pivotal for the last 17 years, court analysts said yesterday.

While that change may not be visible immediately, scholars agree, the ascension of Rehnquist and the addition of equally conservative Judge Antonin Scalia would mean a conservative wing that is expected to be better able to pick up centrist votes, to build and hold the majorities they will need to accomplish their agenda.

Whether that agenda is fulfilled, however, would depend on whether Rehnquist, who has often found himself alone in dissent for much of his 14 years on the court, will be willing to moderate his views to accommodate the center and yet lead the court where he wants it to go. It will also depend on how President Reagan and his successor fill the numerous vacancies on the court that are expected to occur in the next five years.

The court would see an aging liberal wing -- Justice William J. Brennan Jr., 80, and Thurgood Marshall, who turns 78 in three weeks -- under assault as never before by a conservative wing energized with substantial intellectual firepower.

And it would see the more centrist justices -- Harry A. Blackmun, Lewis F. Powell Jr., John Paul Stevens and, on occasion, Sandra Day O'Connor -- courted and appealed to as never before by two charming, exceptionally bright and committed conservative ideologues.

The immediate change may be seen most quickly in how Rehnquist uses the only real power the chief has over other justices -- the ability, when he is in the majority, to designate who will write the court's opinions.

"The big difference between the court under Warren Burger and the court under William Rehnquist," said Harvard Law School professor Susan Estrich, would be a "much sharper strategic use of the assignment power" to make sure the court would move to the right. The new chief, she said, "has a much clearer legal agenda and will assign opinions to justices to further it, versus Burger's equally conservative but much less defined vision of where he wanted the court to go."

The justices gather in conference to vote on cases shortly after oral argument. After those votes, the most senior justice in the majority assigns the opinion-writing.

Where Burger's opinion assignments often seemed based on personal preferences, she said, Rehnquist's would almost certainly be geared to further his agenda, reserving for himself not necessarily the most visible cases, but the ones most likely to move the court in his chosen direction.

Estrich, a former Supreme Court clerk, said Rehnquist's opinions generally would be scrutinized for the innocuous-seeming "zinger" that turns out to be a significant legal change. Burger's opinions, on the other hand, have been checked more for flaws than for groundbreaking analysis, she said.

"Move the court's strategic thinker into the chief judgeship, someone whose prime concern is a vision of the Constitution, who attacks that concern with vigor and intelligence," she said, "then add a new voice, Scalia's, who shares that vision with an intellectual vigor that surpasses anything before," and the change could eventually be substantial, she said.

For the moment, Rehnquist would not have the votes he needs. The building process would take time and likely at least one or more Reagan appointees, and even then the changes might not be abrupt.

"The court," said former deputy solicitor general Kenneth Geller, "is like a gigantic aircraft carrier. It doesn't turn quickly but moves slowly through the water." Still, Geller said the recent moves would show "as sharp a turn as that court is capable of making with one change in membership," especially a change of one conservative for another. Rehnquist, several scholars pointed out, would replace a chief justice whose main interests lie in improving a rickety court administrative structure. The remaining justices, especially those in the center, have been left to their own devices to forge consensus.

Those days, all observers agreed, are over.

But Rehnquist's ability to move the court may turn on whether he would moderate his views in the new role, and court watchers split on that point.

"I think we may see a moderation in Rehnquist's voting," said conservative legal analyst Bruce Fein. "He may vote in ways that may be different as chief justice in order to line up the votes. He is not going to be solely in the role of staking out a position. Now he has an incentive to maintain control over who is writing an opinion."

Other observers are not so sure. Columbia Law School professor Vincent Blasi predicted that "Rehnquist will march to his own drummer. Burger did not want to be in dissent."

Blasi noted that Rehnquist has always staked out his positions quite clearly, staying with them no matter what.

Blasi, who called Rehnquist a "strong infighter," forceful and energetic, said that with Scalia's help he may be able to move the court without altering his views much at all. Much of the moderate nature of the Burger era, Blasi said, may have been due to Burger's weak leadership.

But University of Chicago law school professor Geoffrey R. Stone said he felt that there may be "a lot more importance attached to who is the chief than should be."

The other justices all have "considerable egos in their own right. I don't think Rehnquist is going to be a leader," the former high court law clerk said. "Maybe if he had two more Scalias," Stone added, "but now, the truth is Rehnquist only has three votes or maybe two and a half, depending on where you put O'Connor, and I don't see Rehnquist, given this makeup of the court, being a leader."

Stanford law professor Gerald Gunther agreed, saying, "I don't see the alignment shifting immediately." But Gunther said Rehnquist and Scalia would have a substantial impact on the court even if Reagan makes no other appointments and the Democrats win the White House in 1988.

"Even if Rehnquist and Scalia become the great dissenters," he said, "their views, articulately, crisply put, will be on the books and will be around for the next conservative wave."

Even in the short run, Gunther said, "you do have a bunch of people who are not ideologues," whose votes have been "up for grabs." Of the justices in the center, he said, "to the extent that talking to them and making tough, clear, logical arguments can persuade them in a group of cases, the added intellectual firepower may well make a difference in the short run as well."