A state seeking to send a person involuntarily to a mental institution for an indefinite stay must provide "clear and convincing" evidence at a civil commitment proceeding that the person is mentally ill and a danger to himself or the community, the Supreme Court ruled 8 to 0 yesterday.

The ruling imposes that standard on Maryland, Virginia and numerous other states where neither the legislatures nor the courts have defined the constitutional rights of a person facing commitment against his will. The stricter standard for criminal cases, proof beyond a reasonable doubt, is "inappropriate," Chief Justice Warren E. Burger wrote for the court. Given "the uncertainties of psychiatric diagnosis, it may impose a burden the state cannot meet and thereby erect an unreasonable barrier to needed medical treatment," he said

But the criminal law standard, used in the District of Columbia and 10 states, will remain in effect unless modified.

The decision was the first recognition by the court that a civil commitment to a mental hospital is a significant deprivation of liberty that requires the protection of due process of law guaranteed by the Constitution.

For a person facing such a commitment against his will, Burger said, "it is indisputable" that there can be "adverse social consequences . . . Whether we label this phenomena 'stigma' or choose to call it something else is less important than that we recognize that it can occur and that it can have a very significant impact on the individual."

The court acted in a case from Texas, which is the only state other than Mississippi that allows an involuntary, indefinite commitment under a relatively easy standard of proof, a mere preponderance of the evidence.

Robert Plotkin, attorney for the privately funded, nonprofit Mental Health Law Project, praised the decision while expression regret that it didi not impose the tough criminal law standard.

The "clear and convincing" standard is in effect in 20 states. Three others use the standard of clear, "cogent" and convincing. Two more use clear, "unequivocal" and convincing. The use of "unequivocal," Burger wrote, "is not constitutionally required, although the states are free to use that standard."

Plotkin, whose project represented the Texas patient in yesterday's case. Frank O'Neal Addington, said that the court left for another time questions such as whether a person facing involuntary, indefinite civil commitment has a right to counsel or to a jury trial.

In addition, the ruling provides no reliable clue as to how the court will decide two pending cases in which the issue is the rights of children whose parents seek to commit them to state institutions for the mentally ill or retarded.

Addington, in a six-year period starting in 1969, was committed to Texas state mental hospitals temporarily six times and indefinitely twice.

In December 1975, after his arrest on a charge of "assault by threat" against his mother, she petitioned health officials to commit her son indefinitely.

Resisting, Addington retained a lawyer who, at the end of a six-day trial in Galveston County, asked the judge to instruct the jury to decide whether the evidence showed "beyond a reasonable doubt" that his client was mentally ill and, separately, that he should be confined.

Instead, the judge directed the jury to decide whether the evidence was "clear, unequivocal and convincing." The jurors decided it was. An appeals court ruled, however that Addington, facing a possible lifelong loss of liberty, was denied due process because the standard of proof was lower than it would have been for a criminal conviction.

But the Texas Supreme Court reversed, holding that due process would have been satisfied by the lowest applicable standard, "preponderance of the evidence." Yesterday, the high court sent the case back for a new proceeding under the "clear and convincing" standard, which Chief Justice Burger called "middle" and "intermediate".

"Candor suggests that, to a degree, efforts to analyze what lay jurors understand concerning the differences among these three tests or the nuances of a judge's instructions on the law may well be an academic exercise," Burger wrote. But, he said, quoting an opinion in another case, "the standard of proof at minimum reflects the value society places on individual liberty."

Justice Lewis F. Powell Jr. did not participate in the decision.