Moves by Congress and court may lower the wall between church and state. Sharply divided court moves toward 'accommodation,' not 'separation'

The United States Supreme Court has signaled that it may be rethinking its long-established philosophy regarding the separation of church and state. This reassessment came in a decision on a Pawtucket, R.I., case upholding the right of communities to display Nativity scenes.

The ruling could have important bearing on future court deliberations on school prayer, public aid to parochial schools, and other government support of religious practices.

Even those most alarmed by this decision, however, say that it was narrow in scope and made by a slim 5-to-4 majority of the court. Also, it is not likely, many constitutional lawyers say, that the high court will reverse its traditional position on school prayer - regardless of the current public pressure for prayer in the classroom, and congressional activities along these lines.

But the concern of ''separatists'' is strong. Joseph Conn, a spokesman for Americans United for Separation of Church and State, says: ''We are not so much alarmed by the decision itself . . . but by the trend in the court.''

What might that trend be? Simply, the Supreme Court now seems to be saying that government-sponsored religious programs that merely ''accommodate'' religion, rather than ''advance'' it, are not clearly unconstitutional. This is a clear departure from the three criteria first articulated by Chief Justice Warren Burger in 1971. He held that a practice was unconstitutional unless it (1 ) had a legitimate secular purpose; (2) did not advance or inhibit religion; and (3) did not create an ''excessive entanglement'' of government with religion.

In its apparent new direction, the court seems willing to accommodate those practices that don't clearly violate the ban on ''establishment'' of a state church.

This week's decision in the Pawtucket case may settle a score of municipal creche controversies across the nation. But others will continue to be disputed. In cases from Denver to Scarsdale, N.Y., city officials have erected Christmas displays, only to have them challenged by civil libertarians and often dismantled by the courts.

Observers say that it is unlikely the Supreme Court will tackle this issue again soon, and that it might have ruled differently in a case that involved religious symbols exclusively. The Pawtucket creche display was accompanied by secular artifacts. City administrators, joined by the Reagan administration, specifically argued that the display was part of a ''secular folk festival'' that represents Christmas to many people, as opposed to a ''religious holiday.''

Justice Burger, representing the majority of the court, agreed. He said that the Pawtucket exhibit was intended ''to celebrate the holiday and to depict the origins of that holiday. These are legitimate secular purposes.''

Dissenting Associate Justice William Brennan, however, flatly stated that the display ''amounts to an impermissible governmental endorsement of a particular faith.''

Separatists like Mr. Conn are more concerned with the possible trend - as well as the message being sent by the court to the public and Congress - than with the decision itself.

The high court recently agreed to review a little-heralded but key church-state case from Michigan which involves public payment of parochial schoolteacher salaries for instructing classes on nonreligious subjects. Lower courts have ruled that this practice is in conflict with the First Amendment of the Constitution. Separation advocates wonder if the Supreme Court will now see this as an ''accommodation'' rather than an intrusion.