THE SUPREME Court, which just two years ago overturned a wide array of state restrictions on abortion, has agreed to take another look at the issue, and neither side in the argument can figure out what the justices may be up to.

In its 1983 decision in City of Akron v. Akron Center for Reproductive Health, the court, voting 6-to-3, reaffirmed its decision a decade earlier that women have a constitutional right to abortion. Abortion- rights advocates hailed the ruling as a signal that the court was not about to retreat, despite the furor spawned by Roe v. Wade, the decision which affirmed a woman's constitutional right to an abortion.

But last month, the justices agreed to review a Pennsylvania law that closely parallels the Ohio law overturned in Akron, including provisions imposing a 24-hour waiting period, requiring that doctors recite a detailed description of the detrimental effects of abortion, and mandating that abortions after the first trimester be performed in a hospital.

And this week, the court agreed to hear an Illinois law that requires doctors to inform their patients that certain commonly prescribed contraceptives, such as IUDs and morning-after pills, are actually "abortifacients" that work by causing "fetal death." The law also threatens doctors with criminal prosecution if they fail to use the abortion method most likely to preserve the life of the fetus when there is a "reasonable possibility of sustained survival" outside the womb -- a standard that would permit the state to intervene on the side of the fetus even before the point of viability.

"It is puzzling to try and figure out why the court took the cases," said Nan D. Hunter, a staff lawyer with the American Civil Liberties Union, which is involved in both cases. "It is very disturbing because the cases ought to be governed by principles established in the Akron case two years ago."

"It is puzzling us, too, frankly," said James Bopp Jr., general counsel of the National Right-to-Life Committee. "It's not obvious what is going on."

While the high court has generally agreed to review state abortion laws when one of its earlier decisions left open a particular issue of law, the Pennsylvania and Illinois cases "present issues that are similar to issues that have just been decided by the court," Bopp noted.

Both sides agree that the court is not about to reverse Roe v. Wade. But both, along with academic observers, are busy speculating about exactly what is going on.

Most observers, noting that the high court is more likely to take a case in order to reverse a lower- court ruling, were especially perplexed because in the Pennsylvania and Illinois cases, both federal appeals courts, in striking down the laws, relied on recent pronouncements from the high court itself.

The court almost never explains why it has agreed to take a case. A number of theories are floating about to explain its actions in these:

The "Five-Justices-Are-Over- 76" theory. This theory has several versions. Under one, the three dissenters in 1983 -- Justices Byron R. White, William H. Rehnquist and Sandra Day O'Connor -- have picked up a fourth vote from Chief Justice Warren E. Burger, who went along with Roe but has never been considered a staunch advocate of the decision.

It takes only four votes to agree to hear a case, but, under this variant, the four expect another justice either will retire or die by next fall and a Reagan appointee will provide the fifth vote they need to scale back earlier rulings.

The flip side of this theory has the liberal contingent on the court -- Justices William J. Brennan Jr., Thurgood Marshall, Harry A. Blackmun, and John Paul Stevens -- seizing the opportunity to firm up their abortion decisions before they leave the court and are replaced by more conservative brethren.

Not too many people take either of these seriously. "The ghoulish theories which anticipate or pray for a rapid change in the court's personnel . . . have nothing behind them," said Harvard Law School professor Laurence E. Tribe. "I don't share the general assumption that the justices who are there are hanging on by their fingernails."

The "They'll Be Sorry When They Wake Up" theory. Under this theory, the justices simply didn't realize what they were doing when they agreed to review the cases -- for example, how closely the Pennsylvania law mirrors the one they had just overturned in Akron. Subscribers to this theory expect the justices to wiggle out of deciding the cases by one of several procedural escape hatches.

The "Eroding Citadel" theory. Roe v. Wade was a 7-to-2 decision. Since then, however, Justice Potter Stewart, a member of the majority, has been replaced by the more conservative O'Connor, who criticized the reasoning behind Roe in a stinging dissent from the Akron decision. With Burger shifting, the dissenters in Roe may feel that another member of the majority is about to fold or at least give ground.

Those voting to hear the cases may be "sensing that there is the possibility of picking up a fifth vote, perhaps from Powell or Stevens," Tribe said. "But who knows?"

"There is a growing uneasiness on the court with the Roe v. Wade decision," said the Right-to-Life Committee lawyer Bopp.

The "Can of Worms/Golden Opportunity" Theory. This is really part of the "Citadel" theory in that it assumes shifting sentiment on the court. Abortion-rights advocates fear that high-court approval of either law would serve as an open invitation for abortion opponents to pass a host of new restrictions.

"What you have happening," said the ACLU's Hunter, "is that the right-to-life movement seeks to take every case to the Supreme Court because to the extent they can try to reopen any of the questions concerning abortion rights, they create the possibility for infringements on that right and . . . keep us on the defensive," Hunter said.

Positive reinforcement from the court, she said, "would open the doors to an enormous number of new laws which they will spend years examining."

Anti-abortion forces are praying for exactly that. "A reversal of either of these two cases on any grounds is a plus," Bopp said, "because it indicates a backing away from the steady expansion and repeated reinforcement of Roe v. Wade, I think you may be seeing a shift and a changing of direction."

The court, said Tribe, "wants to take a second look" at permissible restrictions. "The most plausible (explanation) is that having observed that the issue is still deeply divisive, and not resolved, the court is prepared to take a look at how the lines are being drawn."

Both sides agree that any attempt by the court to tamper with the lines, whether to expand or further contract the power of states to regulate abortion, is certain to touch off new rounds of litigation over the nation's most volatile issue. And some of that, of course, will probably wind up before the Supreme Court.