It's become a better-than-even bet that the Rehnquist Court will go wobbly in the knees when a basic right gets in the way of prosecutorial convenience. So its bending of the Sixth Amendment to facilitate the prosecution of accused child abusers is no great surprise.

What is surprising is the transparently statist cast of the majority argument. In a Maryland case, the Supreme Court ruled last week that when child witnesses are in danger of being ''traumatized'' by the rough and tumble of courtroom confrontation with those accused of abusing them, the testimony (and cross-examination) may be conducted on closed-circuit television.

The Sixth Amendment says, categorically: ''In all criminal prosecutions, the accused shall enjoy the right . . . to be confronted with the witnesses against him.'' The court has amended the amendment. Read it, now, ''In some criminal prosecutions,'' the right shall be enjoyed, ''depending upon the emotional duress the hostile witnesses may experience.''

Justice Sandra Day O'Connor's majority opinion, surely well-intentioned, is a rich study in legal and verbal quibbling which revises not only the Bill of Rights but the dictionary into the bargain.

She invokes the familiar ''balancing test,'' a common way of diluting entrenched rights and privileges when they collide with ''state interest.'' The balancing test, of which no mention is made anywhere in the U.S. Constitution, is an inherently inferior style of legal argument, and when judges invoke it, it's usually bad news for rights and privileges.

When the rights and privileges at issue are minor -- for instance, when your ''right'' to drive must be weighed against a compelling public interest in highway safety -- balancing is appropriate. But the propriety of that test quickly dims when the great rights of life, liberty and property enter the picture, as they do here -- and all the more when the incriminating testimony to be especially privileged is as notoriously manipulable as that of small children.

Child abuse is a heinous crime, made the more repugnant by the fact that the abusers are often trusted friends or relatives of the abused, and by the emotional fragility of the victims. But since heinous crimes naturally whet the appetites of prosecutors, there is more, not less, reason to see that procedural protections remain undiluted. That is why the Bill of Rights speaks so categorically, with abrupt and uncompromising shalls and shall-nots.

Justice O'Connor, however, treats the issue as if it were an everyday matter of choosing between more or less equal ''public policy'' preferences: ''That a significant majority of states has enacted statutes to protect child witnesses . . . attests to the widespread belief in the importance of such a public policy.'' Here is the statist argument in its purest essence: The acid test of a dilution of liberty is how ''widespread'' the belief in it is.

Justice Antonin Scalia's withering response to this shaky line of argument could hardly be bettered: ''For good or bad, the Sixth Amendment requires confrontation, and we are not at liberty to ignore it. ... We are not free to conduct a cost-benefit analysis of clear and explicit constitutional guarantees.''

Sensing, perhaps, that her legal argument is unpersuasive, Justice O'Connor sought to buttress it with an entertaining raid on the integrity of the dictionary. ''The word 'confront,' after all,'' she asserts, ''also means a clashing of forces or ideas, thus carrying with it the notion of adversariness.''

Maybe the justice and her law clerks have discovered one of those modern go-go dictionaries, full of rubbery definitions, where such a ''meaning'' may be found. In fact, however, there is not a speck of reputable historical or etymological evidence for it; not one. The great Oxford English Dictionary on Historical Principles, which gives the historical contexts in which English words have been used down through the years, establishes beyond peradventure what the writers of the Sixth Amendment meant by ''confront.''

They meant come face to face with, literally and physically -- not some mushy ''notion of adversariness.'' They meant the kind of face-off that had occurred for years past remembering in English-speaking courtrooms, where one party makes an accusation and the other, eyeball to eyeball, says ''prove it,'' and judge, jury and public watch to see who is the more plausible.

When the Supreme Court begins to wobble on basic liberties, as it does from time to time and as this court often does, there is no substitute for clear voices who know that rights are not for balancing.

Where are you, Sam Ervin, now that we need you?