LET NO ONE doubt the power of disgust--for, for that matter, of anger or pity or outrage -- to influence the United States Supreme Court.

Anyone who does should examine some of the most important cases of the past two terms, starting with the court's July 2 opinion on New York's law against child pornography.

A few days before the decision in New York v. Ferber came down, I told a colleague in the Supreme Court press corps that I was sure the justices would strike down the law as too broad. The statute banned lewd pictures of children under 16, whether legally obscene or not, whether in an art gallery or a dirty movie.

The year before, I remembered, the court invalidated an ordinance in New Jersey that banned all live performances as a way of getting at "nude dancing." It was aimed at strippers but could be applied to ballerinas, the court said, ruling it unconstitutionally overbroad.

My colleague said he thought it didn't matter what the justices had done the year before. He had attended the oral arguments in Ferber. "You should have seen the justices," he said. "They were really offended, really angry. They just took the guy apart. You know what he was charged with, don't you?"

I checked the briefs and the transcript of the oral arguments. Paul Ira Ferber was charged with peddling films of young boys masturbating. At oral arguments, the justices were indeed angry, snapping at Ferber's lawyer from the outset.

On the other hand, we are cautioned by justices not to try to guess the outcome of cases by their reactions at oral argument. Some also still talk about "neutral principles," and about how personal predelictions (what a justice had for breakfast that morning, as Potter Stewart says scornfully) play no role in their work.

On July 2 my colleague's instincts proved correct. The court upheld the New York law in a sweeping opinion making a major exception to its First Amendment rules allowing the banning only of materials judged legally obscene.

Every one of the justices, even the most zealous guardians of the First Amendment, agreed on the judgment. And Justice Byron R. White's opinion left no doubt that something other than constitutional law or, to be fair, something in addition to constitutional law, was at work: Call it the disgust factor.

For example, Footnote 1, Page 1 -- usually reserved for some dry recounting of the status of the case -- described the results of a survey of more than 260 magazines that "depict children engaging in sexually explicit conduct," ranging from "lewd poses to intercourse, fellatio, cunnilingus, masturbation, rape, incest and sado-mashochism."

Footnote 9 talked about the inability of sexually exploited children to develop "healthy affectionate relationships in later life." And so on.

Justices don't talk about their opinions. But it seems fair to say that in New York v. Ferber, an important component of a major First Amendment ruling was outrage.

Last term, the court's rage produced another landmark. This time the focus was not a pornographer but an ex-CIA agent, Philip Agee, who was going around exposing the names of undercover CIA operatives, placing them in potentially life-threatening situations.

The opinion of Chief Justice Warren E. Burger quivered with anger at Agee's activities as it upheld the State Department's decision to revoke his passport and, in the process, dramatically expanded the government's power to restrict the travel of its citizens when it doesn't approve of their overseas behavior.

Is this jurisprudence, as scholars like to call it, the "science" of law? Or was this a tantrum?

How would the court have addressed a hypothetical question as to whether the government can deny foreign travel to people who publish information the government considers detrimental?

The courts do not answer hypothetical questions. The most fundamental requirement of our system is the presence of a "case or controversy," preferably a "live controversy," a phrase that evokes the vitality of the process, the flesh and blood of it. The conflict, wrote Chief Justice Charles Evans Hughes in 1937, must be "real and substantial."

The requirement protects the justices from some of their own hermetic instincts. The isolation they enjoy could become near total without it. It is the next best thing to being there.

It has at times meant assent to hysteria. Hypothetically, again, would any judge have said the governmnet could lock up citizens because of their ancestry? The Supreme Court allowed that during World War II when confronted with the internment of Japanese-Americans.

But it also accommodates compassion.

Consider another of this term's unanimous judgments, Youngberg v. Romeo, which extended limited but nonetheless real constitutional protections to the institutionalized mentally retarded. After hearing about the plight of Nicholas Romeo, the profoundly retarded 33-year-old subject of the case, shackled and abused in a state hospital, even Justice William H. Rehnquist, the constitutional scrooge of the court, went along.

Consider also Plyler v. Doe, another landmark from the past term. The ruling struck down a Texas law requiring illegal alien children to pay tuition in order to attend public schools. It surprised observers, for this court has been stingy in recent years in creating new constitutional entitlements. The climate just hasn't been right. And in 1978, the court said that there was no constitutional right to an education.

The facts of the case, however, confronted the court with tens of thousands of Mexican children, many of whom would be in this country for years, regardless of how the court ruled, and none of whom were responsible for the misconduct of their parents.

That moved the court. It's 5-4 opinion rested on the innocence of the children. They were not responsible for the misconduct of their parents, the court said. They should not be punished for it.

Justice Lewis F. Powell Jr., a conservative man, felt the need to explain himself in a separate statement."I agree with the court that their children should not be left on the streets uneducated," he said.