A sharply divided Supreme Court yesterday made it much harder for authorities to remove children from parents accused of abuse or neglect.

The court, saying that "few forms of state action are both so severe and irreversible" as the termination of parental rights, voted 5 to 4 to require clearer and more convincing proof of mistreatment before children can be permanently removed from their parents.

Justice Harry A. Blackmun said that the proof required in many states has been too lax and too subjective, no more stringent than that required in an ordinary lawsuit over a piece of property. The parent-child relationship, Blackmun said, "is far more precious than any property right."

The ruling resolves one of the most controversial and difficult issues the court has faced in recent years. It was sought by civil liberties and legal aid groups, who argued that many of the parents who lose their children in parental rights proceedings are poor and no match for the combined resources of local government.

State officials and social workers, who proceed against thousands of allegedly abusive parents each year, opposed a heightened standard of proof, saying it would rob them of the flexibility to deal with situations where the physical and mental well-being, even the survival, of children is at stake. Blackmun's decision also took the court deep into family law, a sphere ordinarily reserved for state courts.

The four dissenters, led by Justice William H. Rehnquist, attacked the ruling in unusually strong terms as the beginning of an unwarranted "federal court intervention" in the affairs of the states, a "federalization of family law."

Thirty-three states and the District of Columbia already observe the requirement imposed by the court yesterday. Maryland and Virginia do not, according to the opinion.

Yesterday's case began in 1973 when social work authorities in Ulster County, N.Y., moved against Annie and John Santosky II, then the teen-aged parents of three children from 3 days to 3 years old. Officials temporarily removed the children to foster homes following reports of bruises, abrasions, cuts, pinpricks, blisters and other wounds on the two older children. One was also suffering from malnutrition. They removed the newborn as a precautionary measure.

County officials said they then provided counseling and training to the parents in hopes that the children could some day return. But after three years and--in the view of officials--no progress, authorities went to court seeking permanent "termination of parental rights." The question in yesterday's case was how much proof authorities needed of the alleged abuse to permanently take the children from the Santoskys.

The law generally recognizes three levels of proof, depending on the seriousness of the allegation and the consequences of the finding. The most stringent is proof "beyond a reasonable doubt" required to send someone to jail. The least demanding is proof "by a preponderance of evidence."

"Clear and convincing evidence" is a middle level and has been required by the court, for example, for proceedings committing people involuntarily to mental institutions.

The standards, though subjective measures of certainty, can make an important difference to judges in making decisions.

New York used the least stringent standard, the same required when two parties are quarreling in court over money.

"The fundamental liberty interest of natural parents in the care, custody and management of their child does not evaporate simply because they have not been model parents or have lost temporary custody of their child to the state," Blackmun wrote in his 23-page opinion, based on the due process clause of the 14th Amendment.

"Even when blood relationships are strained, parents retain a vital interest in preventing the irretrievable destruction of their family life," he said.

The "social costs of even an occasional error is sizable," Blackmun said. The parents lose their children forever and are officially branded as "unfit."

The new standard--clear and convincing evidence--is no more stringent than that required to suspend a driver's license, Blackmun wrote. "We cannot believe that it would burden the state unduly to require that its factfinders have the same factual certainty when terminating the parent-child relationship as they must have to suspend a driver's license."

Blackmun was joined by Justices William J. Brennan Jr., Thurgood Marshall, Lewis F. Powell and John Paul Stevens.

Dissenting with Rehnquist in Santosky vs. Kramer were Chief Justice Warren E. Burger and Justices Byron R. White and Sandra Day O'Connor.

Rehnquist agreed with Blackmun that the court could not be "blind" to fundamental liberties, even when states' rights were involved. But family law--divorce, custody, parental rights--"has been left to the states from time immemorial, and not without good reason."

Although New York used the lowest standard of proof, Rehnquist said it protected the parents with a broad variety of hearings and other procedural safeguards, including provision of a lawyer, and with years of effort to rehabilitate problem parents before termination.

The Santoskys, who have since had two more children, now must return to court for a determination of their fitness under the new standard.