The Supreme Court yesterday struck down a Kentucky law requiring the posting of the Ten Commandments in public school classrooms.

The justices ruled, 5 to 4, that the posting was a form of state-sponsored religious indoctrination prohibited by the Constitution. The court rejected the argument that the Commandments are so much a part of western law and culture as to be secular in purpose.

They are "plainly religious," the court said, and may "induce the schoolchildren to venerate and obey the Commandments.

"However desirable this might be as a matter of private devotion, it is not a permissible state objective."

Justices Potter Stewart and William Rehnquist dissented from the opinion. The Constitution does not require "insulation" from religion in schools, Rhenquist wrote. Kentucky "was permitted to conclude that a document with such secular significance should be placed before its students. . . ."

Chief Justice Warren Burger and Justice Harry Blackmum objected to the unsigned majority opinion because it was issued without hearing full arguments.

The unusual Kentucky law, enacted in 1978, required the permanent posting of the Commandments in every public elementary and high school classroom. Because of prior Supreme Court rulings banning prayer and Bible reading in the classroom, the state's action was considered constitutionally shaky from the start. The legislators tried to avoid an unfavorable high court ruling by having the 16x20-inch copies of the Commandments paid for with voluntary contributions and by including this notation: "The secular application of the Ten Commandments is clearly seen in its adoption as the fundamental legal code of western civilization and the common law of the United States."

The American Civil Liberties Union challenged the law (Stone et al vs. James B. Graham, superintendent of public instruction of Kentucky) on behalf of a Quaker, a Unitarian, a rabbi and a woman who professed no religion.

The court said yesterday that "the Ten Commandments is undeniably a sacred text in the Jewish and Christian faiths, and no legislative recitation of a supposed secular purpose can blind us to that fact."

"The Commandments do not confine themselves to arguably secular matters, such as honoring one's parents, killing or murder, adultery, stealing, false witness and covetousness. Rather, the first part of the Commandments concerns the religious duties of believers: worshiping the Lord God alone, avoiding idolatry, not using the Lord's name in vain and observing the Sabbath day.

"This is not a case in which the Ten Commandments are integrated into the school curriculum, where the Bible may constitutionally be used in an appropriate study of history, civilization, ethics, comparative religion or the like," the justices said.

And it does not matter that the copies are financed privately, they said: "The more posting of the copies under the auspices of the legislature provides the official support of the state" prohibited by the constitutional ban on state establishment of religion.

Rehnquist, dissenting, compared the Kentucky law to Sunday business closing laws, which have been found constitutional though they "overlap with what some may see as a religious objective. . . ."

"The Establishment Clause does not require that the public sector be insulated from all things which may have a religious significance or origin," he wrote.

In other action yesterday, a unanimous court ruled that judges' immunity from civil rights suits does not extend to people who conspire with a judge. The ruling means judges may be exposed to scrutiny and required to testify in civil suits even though they may not be held liable for damages in connection with their judicial actions.

The case (Dennis vs. Sparks) originated in Texas, where a corporation sued a Duval County judge over an injunction blocking its production of minerals on land it owned. The corporation charged that the judge blocked the production as part of a conspiracy with a competing company.

Civil rights suits are directed at public officials. The 5th Circuit Court of Appeals ruled that since the public official in this case -- the judge -- was immune, a civil rights suit was impermissible, and dismissed the suit against the judge and his alleged conspirators.

Yesterday the high court ruled the judge's immunity did not shield the private parties from suits. This may mean that judges will have to testify and that they could have their conduct on the bench exposed in a civil trial. But, the court said, "judicial immunity was not designed to insulate the judiciary from all aspects of public accountability."