WASHINGTON — The Supreme Court ruled Tuesday that states may not exclude religious schools from tuition grants that support other private schools.

The justices, by a 5-4 vote, decided that denying grants to students in church schools amounts to unconstitutional discrimination against religion.

The decision is a victory for advocates of school choice, and a setback for those favoring strict interpretation of the principle of church and state separation.

Montana, like more than 30 other states, has a long-standing state constitutional provision that forbids spending tax money to support churches and their affiliates. On that basis, the state supreme court blocked a state-sponsored scholarship program that would give grants to parents sending their children to private and parochial schools.

But the U.S. Supreme Court, in Espinoza vs. Montana, reversed that ruling on the grounds it violated the First Amendment’s protection for the free exercise of religion.

The court did not say states must fund private schools. But if a state chooses to support private schools through grants or scholarships, it may not exclude some of them because of their religious affiliation.

“A state need not subsidize private education,” Chief Justice John G. Roberts Jr. wrote for the majority, including the four other conservative justices. “But once a state decides to do so, it cannot disqualify some private schools solely because they are religious.”