The Supreme Court, which last year seemed to take a sharp turn to the right, this year returned to a more centrist position, deciding almost half of its civil liberties cases in favor of individual rights and pointedly reaffirming the separation of church and state.

And, although the court generally upheld the police powers of the states and the federal government, the justices did expand a handful of the landmark Warren court cases granting rights to criminal suspects.

During the 1984-85 term that ended last week, the moderate center that has dominated the court for most of the last 16 years eased the court back to its traditional moderate position.

Civil libertarians expressed elation, while the Reagan Justice Department puzzled over what went wrong in its effort to push a conservative agenda. U.S. Solicitor General Rex E. Lee said the administration had some "major disappointments this term," especially in its effort to lower constitutional barriers between church and state.

In four major cases, a narrow majority voted to draw a solid line between the government and church schools. A 5-to-4 majority ruled not only that a Michigan program of open-ended aid to parochial schools was unconstitutional, but also, in the term's biggest surprise, that New York City could not use federal funds to send public school teachers into religious schools under a program to help disadvantaged students.

American Civil Liberties Union legal director Burt Neuborne, who called last year's court record "truly appalling," said that the court has "returned to the role it has played historically as a defender of the individual."

What "the trend people thought they saw last term," when the court came down with a host of conservative decisions, "did not materialize," he said.

The difference between the two terms was the court's key swing vote, Justice Lewis F. Powell Jr. Powell sided with conservatives consistently during last year's term, but this year pulled in the opposite direction.

Powell tipped the scale in virtually every close vote. He was on the losing side only six times in 89 decisions in which he participated this term. In 18 cases where the court split 5 to 4, Powell was in the majority 14 times.

Neuborne said Powell's position leaves the 78-year-old Virginian "the most powerful individual in America." Powell, a moderate appointed by President Richard M. Nixon, sided with the liberals this year more than he has in any of his 14 years on the court.

Conservatives such as Bruce E. Fein, who analyzes the court for the American Enterprise Institute, said last week that he was surprised when the administration "suffered severe defeats" in several areas in what he called a term of "pause and irresolution."

Fein said conservatives had every reason to be optimistic last fall that the court would lower the barriers to church-state separation. The Supreme Court in recent terms had approved a city government-sponsored Christmas nativity scene, state tuition tax deductions for religious schools and a state-paid chaplain for the Nebraska legislature.

"Everything that seemed to have been won," Fein said last week, "went out very quickly," as the court, in addition to the parochial school cases, reaffirmed its disapproval of teacher-led prayer in public schools and struck down a law that gave employes who are religious greater rights than nonreligious workers.

"State officials misread the court as having moved all the way toward the authoritarian end of the spectrum," said Harvard Law School Professor Laurence H. Tribe, a prominent constitutional scholar.

"It was teetering" last year, Tribe said, "but it had not gone all the way." Conservatives were pushing the justices "so far so fast that they may have recoiled from an invitation to join the new right. It was an offer the court could readily refuse. Having smelled victory, the right pushed the court over the brink."

The Reagan administration nevertheless won a substantial number of cases in which the justices backed executive branch prerogatives, and the administration generally had its way in criminal cases, although there were notable exceptions.

Justice Department figures show the government won 80 percent of its cases overall, down from an extraordinary 87 percent a year ago. But the cases it lost this year often were the most important cases, a reversal of last year's record.

Overall, the justices this term gave much greater weight to individual rights as opposed to government power.

Last year the court handed down signed opinions in 69 civil liberties cases. It decided 13 in favor of the individual and 56 in favor of the federal or state government. The government's 81 percent rate was the highest in nearly five decades.

This term, the court, in 51 decisions involving similar constitutional claims, ruled 29 times -- or 57 percent -- for the government and 22 times for the individual. That government success rate is actually lower than its average for the five years preceding last term.

In four other cases, with Powell absent due to illness, the court split 4 to 4, upholding an appeals court ruling that sided with the individual's constitutional claims against the government. A tie vote does not set a constitutional precedent.

In two other cases, the court upheld individual free speech claims, but not on constitutional grounds.

If these two cases and the tie cases are counted, individuals with civil liberties claims won nearly half the time before the Supreme Court, a record not seen since the days of Chief Justice Earl Warren.

The court continued to favor law-and-order views, but individuals won a number of significant cases as the states, although not the Justice Department, seemed to misread how far the justices were prepared to go.

In several cases, the court extended Warren court precedents and expanded suspects' rights. It ruled that indigents pleading insanity had the right to a court-appointed psychiatrist, that indigents appealing convictions had the right to a court-appointed lawyer, that police could not use deadly force to stop a fleeing felon except where there was a danger to the public, and that prosecutors could not force a suspect to undergo surgery to remove a bullet sought as evidence.

On the other hand, the justices continued to uphold prison officials' prerogatives, to give police greater freedom to act without warrants and to chip away at the 20-year-old Miranda rule requiring police to read suspects their rights.

Last year the court created a "public safety" exception to Miranda. This year, it said a confession induced before Miranda warnings are given is not usable in court, but a second one obtained after the warnings are issued could be used against a suspect.

The court was sympathetic to individual claims of discrimination by state governments. In the most significant of them, the court struck down zoning laws that barred a group home for the mentally retarded, but not for anyone else.

While the court insisted it was doing nothing new, Tribe, Fein and Neuborne were adamant that the case, in Tribe's words, "reinvigorated equal protection." The case, they said, likely will make it tougher for government to justify laws that treat some groups, such as the retarded, differently than others.

In a major case involving the balance of power between the states and the federal government, Justice Harry A. Blackmun, a centrist, changed his mind this year and the court decided that the 10th Amendment did not protect states from federal laws regulating the wages and hours of state or local employes. The case overturned a ruling nine years ago, in which Blackmun voted the other way.

Although that was seen by some observers as a major blow to states' rights, others, such as former deputy solicitor general Philip A. Lacovara, see the court last year as generally sympathetic to state prerogatives, especially in economic regulation, so long as the states play fair.

The court, Lacovara said, generally struck down state laws that discriminated among their own residents or set up distinctions between state and out-of-state residents. It overturned residency requirements for a tax break for veterans, residency requirements for lawyers and breaks for local, as opposed to out-of-state, insurance companies.

But while the justices several years ago exposed local and state governments to a barrage of antitrust suits, this term the justices heightened protections against such suits in two cases that "much more directly affected pocketbooks," Lacovara said. "Where there is elbow room to interpret federal statutes in favor of state autonomy, the Supreme Court gives states the benefit of the doubt."

The last term seemed quieter than recent terms. There were fewer signed opinions -- 140 as opposed to 151 in each of the preceding two terms -- and a number of important cases were decided by tie votes because of Powell's absence. He missed 56 cases because of surgery for a cancerous prostate.

The justices also ducked constitutional questions whenever possible, deciding several major cases on narrow grounds that resolved the individual case but did not touch on broader questions.

The term has already sparked debate among law professors over whether last year was an aberration or this year was the calm before a conservative storm.

A year ago, Tribe said, the court was "on the precipice and no one could say whether it was going to leap or step back." This term was a source of relief to civil libertarians because the court stepped back.

But the most recent term "should not lead them to breathe easily," Tribe warned. It is a "dicey situation" with a court that is deciding things on a case-by-case basis and in close votes.

Conservatives said they hope that one or two key Reagan appointments will make the difference. Although the justices appear to be in good health and seem bent on staying on the court as long as they can, five of them are over 76.