Washington — Discerning a pattern in the decisions announced by the US Supreme Court in a single term is always a bit like working an ill-fitting jigsaw puzzle. The pieces never fit perfectly.
The court provided an apt example of this last Friday, the last decision day of its current term.
The Court upheld New York's law against child pornography. It held that civil-rights boycotters are protected by the First Amendment from monetary penalties for their actions. And it struck as unconstitutional part of Florida's death penalty law.
The first decision is ''conservative'' and the second is ''liberal.'' But the court was unanimous on both. The third, reached by a five to four vote, revealed the fragile balance within the court on certain key questions - a balance which shifts with the facts of particular cases and which a single new member could tip.
It is too soon to accurately assess the role which Justice Sandra Day O'Connor has taken in the court's rulings. But a look at the major decisions reached by the justices during her first term shows a number of definite trends. The court is now even more strongly disposed than in the 1970's to back police, judges, and prosecutors rather than defendents in criminal cases. And it favors giving more and more power to state and local officials, restricting intervention by federal officials and federal judges.
At the same time, the court continues to be protective of certain ''under-classes'' in society - aliens, women, and mentally retarded persons. And it adopts a liberal stance on most questions of First Amnedment freedoms and individual rights. Criminal Law
The court is deeply divided on questions of criminal law. Of 18 rulings in this area during the term, only one was unanimous.
The justices did clarify an area left murky by earlier decisions, confirming the power of police to search the contents of a car or a suspect's room without a warrant, if they have probable cause to stop the car or arrest the suspect. The Constitution's protection against double jeopardy and it's guarantee of a speedy and fair trial received narrowing interpretations from the current court.
On the other hand, the liberal view prevailed on the two most controversial issues - capital punishment and the exclusionary rule. By a five to four vote, the court limited further the circumstances under which a death sentence is constitutional, and it insisted that prosecutors not use illegally obtained evidence in court. State power
The balance between state and federal power came before the justices in a variety of cases during the term. Although there was no clear winner or loser in these matters, it was evident that advocates of state power are gaining strength.
The justices upheld New York's child pornography law and California's anti-busing measure. They struck down Illinois's business take-over act, New York's standard for terminating parental rights, and Alaska's scheme for distributing oil revenues to its citizens.
In a long list of little-noticed rulings, the court told federal judges to defer to state courts on questions as diverse as job discrimination, state tax disputes, constitutional challenges to state criminal convictions, local labor disputes, custody fights, and attorney discipline proceedings.
The court held that the Constitution denied states the power to ban the export of electric power or ground water. And the justices, closely divided, upheld as constitutional a 1978 law which directs states to improve the efficiency of energy consumption by their residents. The four dissenters in this case argued forcefully that this law went too far in its interference with state business. Individual rights
In a major expansion of the Constitution's protections for the individual, the court - again divided five to four - held that states must provide illegal alien children with a free public education. The disagreement between the judges highlighted a basic question that divides the current court: What is its proper role in addressing such social problems?
The justices agreed that these children, once present in this country, should be educated at public expense. But they disagreed over who should take the lead in this task. The majority assumed that it was the court's responsibility in light of the fact that Congress had not ''provided effective leadership in dealing with this problem'' of illegal aliens. In dissent, Chief Justice Warren Burger responded that ''it is not the function of the judiciary to provide 'effective leadership' simply because the political branches of the government fail to do so.''
The court found California's anti-busing initiative within the limits of the Constitution, but struck down Washington state's anti-busing law as impermissible. The justices found that Congress had authorized federal officials to oversee the employment practices of schools receiving federal funds. And they held that the Constitution guaranteed mentally retarded persons in state institutions a certain level of safety, freedom of movement, and training.
The court held that American subsidiaries of foreign companies must comply with federal equal employment laws. And other recent rulings make it more difficult for employers to defend themselves against charges of job bias.
In another little publicized trend, the court moved to stem the flood of damage suits against federal officials by persons who claim that their rights have been violated by some official action. In the most noted decision in this area, the court held that presidents - including former President Nixon - are absolutely immune from such suits. In a companion case, the court set a new standard for suits against subordinate officials who do not enjoy absolute immunity, making it easier for them to defend themselves by showing that they acted in good faith. First Amendment
The court further expanded the boundaries of First Amendment protection during the term, ruling that the First Amendment applies to school board decisions to remove books from school library shelves. That amendment, the court held, also protects civil rights protesters against damage judgments. The court ordered a trial in a book banning case from Long Island, and reversed a million-dollar damage judgment against the NAACP. That damage award had been granted by a Mississippi court to merchants who had suffered substantial losses as a result of a 1966 civil rights boycott of their stores. Child pornography was placed outside the bounds of First Amendment protection, as the court upheld New York's law making it a crime to distribute such material.
States may not require judges to close sex-crime trials to press and public when minor victims testify, the court ruled in a Massachussetts case. The justices found that the University of Missouri abridged the guarantee of freedom of religion when it refused to allow a conservative student religious group to use a classroom for its regular meetings. The court also held that despite his religious opposition to the social security system, an Amish farmer who employed other Amish must pay social security taxes on their wages.