In his 33 years, Nicholas Romeo has not been given much. Recently, however, he, and approximately 135,000 persons similary situated, acquired some rights.

The word "landmark" is used too casually concerning Supreme Court rulings. But in its ruling in Romeo's case, the court stepped, gingerly but unanimously, into new territory. For the first time it has affirmed substantive rights of involuntarily committed retarded persons in institutions. In this context, "involuntarily" does not mean against the individual's will, but rather that the individual's will was not engaged.

Romeo is profoundly retarded. Since the death of his father seven years ago, he has been a resident of Pennsylvania's much-criticizes Pennhurst institution. He cannot talk and lacks basic self-care skills. When petitioning for his admission to Pennhurst, his mother said: "He becomes violent -- kicks, punches, breaks glass. He can't speak -- wants to express himself but can't."

In Pennhurst, he was injured 63 times, by his own violence or that of other residents, in the two years before his mother went to court. When in Pennhurst's infirmary for treatment of a broken arm, he was physically restrained in bed during parts of the day, with "soft" restraints on his arms. The staff said this was not for punishment but for his protection, and that of other patients.

Now the court has held that there are constitutionally required conditions of confinement, derived from the 14th Amendment. The ruling is a delicate assertion of judicial oversight, tempered by assertions of deference to professionals in the field of institutional care.

The opinion, written by Justice Lewis Powell, affirms three rights: to safety, to freedom of movement and to training. The first two "needs" are rights conditioned by institutional necessities, and the right to training is defined, minimally, as training necessary for enjoyment of the first two rights. But Romeo claimed only a right to "minimally adequate habilitation."

The court calls even this claim "troubling," for several reasons. One is that "as a general matter, no state has a constitutional duty to provide substantive services for those within its border." The court says the term "habilitation" is defined neither precisely nor consistently in psychiatry. (Actually, it is unclear how such habilitation is a psychiatric matter.) The court also says that professionals differ "strongly" as to whether effective training of all severely or profoundly retarded persons is possible.

The court does not know what the experience of recent years proves: that pessimistic prognoses, even by professionals, concerning all kinds of retardation, are apt to be wrong (although, alas, somewhat self-fulfilling). But the court knows that an institutionalized person requires rights -- enforceable claims -- because he or she is wholly dependent on the state.

All Romeo sought, and all the court affirmed, is a right to "training suited to" the two "needs" of bodily safety and minimum physical restraint. The court stressed that "This case does not present the difficult question whether a mentally retarded person, involuntarily committed to a state institution, has some general constitutional right to training per se." The court actually pruned a lower court ruling, which it considered so broad as to permit excessive judicial intrusiveness. The court said there is a "presumption of correctness" regarding the decisions of professionals, who "shall not be required to make each decision in the shadow of an action for damages."

Nevertheless, this ruling will, like a hovering angel, cast a comforting shadow on the approximately 135,000 retarded persons in institutions, many of whom are living in stomach-turning conditions. Furthermore, it expresses, and thereby nourishes, a social sensibility important to 6 million other retarded citizens.

The affecting surge of gratitude among friends of retarded citizens, including friends whose retarded friends are not institutionalized, is perhaps disproportionate to the rights affirmed by the ruling. But the satisfaction is commensurate with the expressive, as distinct from the technical, power of the ruling.

Americans are litigious, but not lawyer-like. American society is not animated by the dry distinctions that characterize judicial craftsmanship. Rulings like this one, and Brown v. Board of Education , the 1954 school desegregation decision, are examples of law's tutelary functions.

In 1954, the elemental message was: blacks are full citizens. In 1982, the message is: retarded people, too, are members of the community that the Constitution constitutes. The fact that these messages have had to be sent down from the Supreme Court -- the Mount Sinai of American government -- is a measure of how bad things were then, and are in some places today.