The Supreme Court yesterday heard a constitutional challenge to a federal law that provides computers, software and library equipment to parochial schools, struggling once more with the circumstances under which government can support religious organizations.

An eventual ruling in the case could have implications for the fractious debate over school vouchers. But while the justices appeared to be leaning yesterday toward upholding a decades-old federal law that furnishes materials to private schools, including religious ones, there seemed to be no consensus for an overarching principle that would govern a bolder mingling of church and state such as publicly financed vouchers to help students attend parochial schools.

The 1965 education law at issue yesterday gives public school districts federal money for special services and instructional equipment and requires the funds to be shared with all private schools in the district. The law has become newly controversial as a result of the Clinton administration's proposal to link all classrooms--including those in parochial schools--to the Internet. After Louisiana taxpayers complained about the funds for computers going to religious schools, the Fifth Circuit Court of Appeals ruled last year that the 1965 law violated the separation of church and state.

The Clinton administration sided with parochial school parents who appealed the ruling, arguing that the high-tech support was a neutral policy that did not support religious indoctrination.

Michael W. McConnell, appearing yesterday on behalf of the parents, urged the justices not to deny students computers that have become "the basic tools" of today's classrooms simply because their parents have chosen to send them to sectarian schools.

Lee Boothby, representing Louisiana taxpayers on the other side, countered that what's at stake is "our historical commitment" against using public money to support religious schools.

He said that unlike textbooks on specific subjects, computers have virtually limitless use and could easily be diverted into a mission of faith.

The boundary between church and state is one of the most difficult areas for the court, and cases on the subject often come down to a single vote. In earlier decades, the justices generally disallowed public funds for educational materials beyond textbooks, such as maps and science equipment. But more recent decisions by the court have permitted more government involvement with religious programs, for example, by allowing public school teachers to provide remedial help at parochial schools.

Justice Antonin Scalia at one point repeated an adage of Sen. Daniel Patrick Moynihan (D-N.Y.), pointing up the confusing standards: If the court allows the government to pay for books but not maps, what becomes of an atlas--"a book of maps"?

A ruling in the case of Mitchell v. Helms is expected next spring.