By a 6-3 vote, the high court declared that allowing a student to deliver a Christian prayer over the loudspeaker before kickoff violates the constitutional requirement on separation of church and state.
Returning to a politically sensitive issue in an election year, the Supreme Court added to rulings in 1962 barring public school prayers in the classroom, and in 1992 barring prayers at graduation ceremonies.
The ruling comes in a case from Sante Fe, Texas, a small community where the school district authorized prayers that do not favor one religion over another.
"This decision is going to stop student-led prayers in their tracks and I'm not sure that there is much that Congress can do about it," said CBS News Legal Consultant Andrew Cohen. "Any federal law the legislators are likely to pass is likely to meet the same fate that befell those students in Texas. An unconstitutional practice is an unconstitutional practice, the justices are likely to say."
Texas governor and Republican presidential nominee George W. Bush favors the prayers struck down in this case, and in fact joined a brief defending them, reports CBS News Correspondent Barry Bagnato. It's likely he'll use the issue on the campaign trail against Democrat Al Gore.
But the author of Monday's important ruling, Justice John Paul Stevens, says these invocations take place on government property at government-sponsored school-related events. Therefore, the court says, they breach the Constitution's wall separatuing church and state.
Writing for the majority, Stevens said: "The policy is invalid on its face because it establishes an improper majoritarian election on religion and unquestionably has the purpose and creates the perception of encouraging the delivery of prayer at a series of important school events."
Stevens said while the court recognizes "the important role that public worship plays in many communities ... Such religious activity in public schools, as elsewhere, must comport with the First Amendment."
Joining Stevens were Justices Sandra Day O'Connor, Anthony M. Kennedy, David H. Souter, Ruth Bader Ginsburg and Stephen G. Breyer.
Chief Justice William H. Rehnquist and Justices Antonin Scalia and Clarence Thomas dissented in a vigorous opinion by Rehnquist.
"Even more disturbing than its holding is the tone of the court's opinion: It bristles with hostility to all things religious in public life," Rehnquist said.
The case originated when four high school students and their parents sued the Santa Fe Independent School District in Galveston County, Texas, in 1995 over its policy of letting students elect a "chaplain" to lead "prayers" at graduation ceremonies and home football games.
Two families - one Catholic and one Mormon - challenged the policy. Their identities were sealed by the courts.
After their lawsuit was filed, the policy was changed to let student-elected representatives no longer called chaplains give a "message or invocation." Speakers are free to choose what they say so long as it promotes good sportsmanship.
A federal appeals court ruled last year that school officials must tell students to keep their graduation-ceremony comments and prayers "nonsectarian and non-proselytizing" but also ruled that student-led prayers at high school football games are always out of bounds.
School officials appealed both parts of the 5th U.S. Circuit Court of Appeals' ruling, but the Supreme Court agreed only to focus on the football games, passing up the graduation-ceremony dispute.
Prayers over the football stadium's public address system were heard at all of Santa Fe High School's home football games last fall. Right after the 5th Circuit court's ruling, a group of Christian students led by senior band member Marian Ward obtained a judge's order allowing that invocations be continued.
Ward, who led the prayers at those games, attended the Supreme Court's argument session in the Santa Fe case in March.