The Supreme Court term that ended Wednesday was one of those few each decade that will be remembered for an extraordinary number of major rulings, but many of them were so narrowly decided that they may turn out to be shaky precedents.

Landmarks were created and undone and questions that matter to a lot of people were answered--on abortion, legislative veto, tuition tax deductions, congressional redistricting, the death penalty, prison sentences, sex and race discrimination, the powers of police and regulatory agencies, and states' authority to tax.

One symbol of the term was the court's difficulty in churning out enough copies of its opinions to fill all the requests.

A more important symbol, however, serves as a reminder of the instability of narrow decisions. During the court's final frenzied week, one majority opinion contained a bizarre footnote attacking the ruling as a "truly radical departure" from the law.

It clearly had been intended to be part of a minority dissent, but someone had forgotten to remove it after the shift of a single vote apparently transformed the dissent into a 5-to-4 majority opinion in Ruckelshaus vs. Sierra Club.

Many of the term's celebrated decisions were extremely narrow. In the often-quoted words of the late Justice Owen Roberts, some seemed like "restricted railroad tickets, good for this day and train only." There is no assurance, as Roberts put it in 1944, that they would not shortly be "repudiated and overruled by justices who deem they have new light on the subject."

The court built itself a "castle of sand," said Bruce Fein, American Enterprise Institute Supreme Court analyst. "When they switch by one or two votes," Fein said, "they can switch back just as easily."

Some experts question whether the term can be considered memorable.

"It was an unusual term" because of the newsworthiness of the issues before the court, said Harvard Law School Professor Laurence H. Tribe.

"But the difference between one important case out of 150 and five important cases is more likely to depend on accidents of timing.

"I also think there may be a little less in the term than meets the eye," Tribe said. "Some of the decisions widely celebrated as landmarks may make less difference than they did news. The Bob Jones ruling upholding the Internal Revenue Service's authority to deny tax exemptions to discriminatory schools will depend on the vigor of IRS enforcement.

"The air-bags case striking down the Reagan administration's rescission of passive restraint requirements for new cars is a reminder that in one case out of a million, the court will find an action by an agency implausible," Tribe said.

But genuine patterns appeared to emerge:

* The Reagan administration tended to fare poorly when it went out on an ideological limb, as it did when it claimed the IRS could not deny tax exemptions to discriminatory schools and when it urged a major departure from the court's rulings on the right to abortion. It tended to do better when it adopted conventional government legal positions, such as greater flexibility for law enforcement authorities.

* In death penalty cases, the court seemed to relax its demands for perfectly crafted statutes and procedures. In four cases, the court appeared to say that fairness--not perfection--is required.

* The court also relaxed its standards for police conduct, permitting warrantless searches and searches without a strong suspicion of a crime in more circumstances than before, especially when drugs may be involved.

* The court limited the ability of public employes to speak out on issues relating to their jobs without fear of retaliation. That decision, in Connick vs. Myers, was part of what the American Civil Liberties Union called "a serious drubbing" taken by public employes this term. Tribe called it "the most important setback in First Amendment right in a number of years."

A second decision curtailed the right of federal employes to exercise constitutional rights and to sue to protect those rights in the federal courts.

* In the tuition tax deduction case and the decision upholding prayers by legislative chaplains, the justices showed continued signs of lowering the church-state "wall" against government establishment of religion.

* In two cases, the court made it easier for independent presidential candidates and small third-party movements to compete.

* Justice Sandra Day O'Connor, who spent much of her first term denouncing encroachments on states rights, proved herself capable of invalidating state laws this term when she wrote opinions striking down California's vagrancy statute and Minnesota's special tax on large newspapers.

Among the 5-to-4 rulings during the term were: a decision declaring sex-based pension and retirement plans illegal; a redistricting ruling requiring near-perfect statistical equality among congressional districts; approval of Minnesota's tuition tax deductions for parents of public and private school students; validation of the District of Columbia's insanity defense law; an opinion striking down, for the first time, a prison term as a violation of the Eighth Amendment's ban on cruel and unusual punishment, and more.

Consider the tuition tax deduction case, Mueller vs. Allen. The primary obstacle to such programs before that decision was a 1973 Supreme Court ruling striking down New York's tuition "grant" program for private schools. Justice Lewis F. Powell Jr. wrote that ruling in Committee for Public Education vs. Nyquist.

But in this year's case, Powell adjusted his views and joined in upholding Minnesota's law, which since 1955 had provided aid to parents of both private and public school students. A single vote made the difference between no aid for private schools and, potentially, substantial aid.

In March, 1980, a 5-to-4 court upheld a life sentence, under a Texas "habitual offender" law, for a man convicted of a total of three minor non-violent swindles with a total value of less than $200.

This term, the court struck down a life sentence imposed on a non-violent repeat offender. The difference betwen the two cases, wrote Powell for the majority in Solem vs. Helms, was that Texas allowed parole and South Dakota did not.

The other, and perhaps more important difference, was Justice Harry A. Blackmun, who voted with the majority in the Texas case and went the opoposite way in the South Dakota case.

Some of the majorities that appeared larger, on closer examination, were not so large. Immigration and Naturalization Services vs. Chadha, which struck down Congress' use of the legislative veto, achieved its result by a 7-to-2 vote, a remarkable ratio for this court.

But the reasons Powell gave for concurring applied only to the single case. Only six justices approved the opinion of Chief Justice Warren E. Burger.

Powell and Justice Byron R. White and, occasionally, Justice John Paul Stevens continue to be "the floating middle" most responsible for shifting the court one way or the other. They function as a kind of mini-court. If two of them take one side in a case, that side generally wins.

The other justices are much more predictable because they are often polarized along conventional liberal-conservative lines. Burger, O'Connor and Justice William H. Rehnquist are most often to the right and Justices William J. Brennan Jr., Thurgood Marshall and Blackmun are generally to the left.

The gap between the extremes remains vast. What to Rehnquist was a perfectly proper death sentence imposed by a Florida judge in one ruling was to Marshall and Brennan a "miscarriage of justice . . . utterly faithless to the safeguards" required by the Constitution.