The First Amendment wall separating church and state was lowered by a few inches this week by the United States Supreme Court. On Wednesday the court approved for the first time a state program providing general aid to parents who send their children to private or parochial schools.
By a 5-4 vote, the court upheld a Minnesota law that permits parents to take a state income tax deduction of up to $500 for tuition, textbook, or transportation expenses for each child in elementary school and up to $700 per child in secondary school.
Although the deduction is available to parents with children in public or private schools, the bulk of the benefit accrues to those with children in private or parochial schools.
Despite that effect, the high court upheld the state law as providing such an ''attenuated financial benefit'' to church-related schools that it did not violate the Constitution's ban on state-established religion.
The ruling was a major victory for advocates of aid for parochial schools, who have watched as the Supreme Court has struck down as unconstitutional a variety of state aid programs in the last dozen years.
Among those programs struck down in the 1970s were some that provided salary supplements to parochial school teachers; reimbursed parochial schools for the cost of administering standardized tests and keeping certain required records; paid for transportation for field trips for parochial school students; and provided tuition grants and tax credits to parents of private school students.
The court majority relied heavily on the fact that the Minnesota tax deduction was available to public school parents as well as private school parents.
Writing for the majority, Justice William H. Rehnquist noted that the breadth of the group that could benefit from the law was ''an important index of secular effect.''
That characteristic was crucial to the majority's finding that the law had a primarily secular purpose: to encourage the development of a well-educated citizenry by aiding parents in paying the rising cost of education.
Justice Rehnquist, joined by Chief Justice Warren E. Burger and Justices Lewis F. Powell Jr., Byron R. White, and Sandra Day O'Connor, also emphasized that ''by channeling whatever assistance it may provide to parochial schools through individual parents, Minnesota has reduced the establishment clause objections to which its action is subject.''
When aid to parochial schools is the result of individual parental decisions, it cannot be said that the state is giving its stamp of approval to any particular religion - or even to religion in general, wrote Rehnquist.
The dissenters, Justices William J. Brennan Jr., Thurgood Marshall, Harry A. Blackmun, and John Paul Stevens, argued that even such indirect state aid to religious education was prohibited by the First Amendment.
They criticized the court for upholding, for the first time, financial aid to religious schools without any guarantee that that aid would not be used to support religious instruction. The net result of that ruling, they said, ''is flatly at odds with the fundamental principle that a state may provide no financial support whatsoever to promote religion.''
The court's decision cleared some of the constitutional questions that have delayed action in Congress on President Reagan's proposal for a federal tuition tax credit. It did not, however, promise clear sailing for such a law. The one-vote margin by which the court upheld the Minnesota law and the majority's careful reasoning made clear that Congress must draft any such bill with great skill in order to avoid constitutional pitfalls.
In addition, the court appeared to say that unless a tax benefit of this type was made available to all parents with schoolchildren, it would not pass constitutional muster. Mr. Reagan's proposal is currently designed to provide a tax credit only to private school parents. If Congress is forced to expand this proposal to offer some benefit to public-school patrons as well, the cost to the US Treasury could greatly increase - a major consideration in these days of mounting deficits.