A GENERATION after the Brown decision, blacks may be the most frustrated of all in trying to convince people - particularly federal courts - that they are victims. Nathaniel jones, general counsel of the financially strained NAACP, puts his finger on this sense of exasperation when he says, "They are asking us to prove that water is wet."

This gets into something that the press and the public tend, at best, to gloss over: Civil rights battles in federal courts today often do not turn, as popularly believed, on whether judges approve a controversial remedy, be it busing pupils between cities and suburbs or "affirmative action" in professional school admissions or in jobs. Increasingly, the more fundamental quarrels are over whether there was ever any violation to begin with, or at least how much of a violation there was.

The Supreme Court, for example, did not question the need for city-suburb busing in the Wilmingto, Del., are. The basic reason was simple: It had been proved that students were deliberately segregated in the suburbs as well as in the city. The Burger court rejected city-suburb busing in the Detroit area: A majority held that a violation by the suburbs had not been proved. The violation, not the remedy, was what made the difference.

So it goes with other cases. The high court has let stand affirmative action plans granted by lower courts, including plans ordering numerical "goals" or "quotas." In a Minneapolis fire department case, for one, the Suprame Court let stand a plan requiring that one minority applicant be hired for every three who qualified, until the department had hired at least 20 minority wookers. Deliberate past discrimination had been proved in the case.

The Bakke case was different in many ways - not least of which was the absence of past racial bias by the medical school involved. The school had almost no history of any kind because it hadn't been open very long, a pivotal point in Justice Powell's swing vote. He ended up agreeing that race could be used as only one factor in student admissions - not to correct any past discrimination, but to ensure a diverse student body, an entirely different issue.

So now we are faced with the equally portentous Weber case in the Supreme Court, and how do you find the Justice Department framing "the central question"? Can an "apparent" violation of civil rights law justify a voluntary affirmative action program of the kind agreed to by Kaiser Aluminum and the Steelworkers union? That agreement required that half those trained in a special program for higher-paying skilled jobs be blacks and women, and it is being challenged by Brian F. Weber, a white male who was denied such training.

This, as widely noted, is a Catch-22 situation union. The company agreed to be affirmative action plan without admitting past discrimination - and was encouraged to do that by the EEOC - so it wouldn't be vulnerable to lawsuits by minority workers seeking back pay. So thre can't be sufficient evidence of a violation that needs fixing.

The point of all this in rough terms, is that you can't argue about punishment until you find out if somebody's been proved guilty - and what's involved in proving that is what sometimes drivers the NAACP's Jones and other civil rights attorneys to distraction.

One thing they are increasingly troubled by is what's happening to "the burden shift." The "burden shift," of course, is not blacks being hosed by Bull Connor's police at James Meredith being turned away from the schoolhouse door. You don't see headlines saying, "High Court Modifies Burden Shift." But that, in fact, is a profound part of what's been going on.

Most of us nonlawyers have long been under the impression that courts consider people innocent until proved guilty. That's not exactly the way it always works. In many cases, judges end up "shifting the burden of proof" to defendants or respondents, who are presumed guilty until they prove themselves innocent.

It's an immense power, often letting judges really decide cases by chosing which side must prove what. It has been used both for and against the oppressed.

In the 1700s in Georgia, for example, courts put the burden of proof on suspected runaway slaves "to show that they were not runaways," as A. Leon Higgenbothm Jr. notes in his impressive study of American race law. "This probably imposed an immense, if not impossible, evidentiary task."

A couple of centuries later, in the Denver school segregation case, the courts used the burden of proof to help black plaintiffs. There the Supreme Court ruled that once civil rights attorneys showed the school board deliberately segregated a "substantial" part of the school system, all Denver school segregation could be presumed intentional (the only kind that's unconstitutional). The school board had the burden of proving itself innocent. It couldn't. That's how the court found that a systemwide offense had been "proved" and that systemwide desegregation was in order.

In fact, a large part of whether you have systemwide busing in the North and West or affirmative action in employment now hangs on this issue. And the Burger court has been tinkering with the burden shift.

The burden of proof is a pivotal issue in the Dayton and Columbus school cases now back before the Supreme Court. As for jobs cases, they've relied heavily on statistic showing low hiring of minorities and women after employment exams, with employers having the burden of proving the tests weren't discriminatory. But the Burger court has now made clear that such statistics by themselves do not automatically shift the burden of proof.

That is an oversimplified description of what has happened. But the point is, as Harvard law professor Laurence H. Tribe puts it, "The burden may be shifting back" to the civil rights movement to prove the intent of those they bring cases against. Many civil rights lawyers believe that popular resentment against court ordered remedies is promting the new caution in how offenses are proved, that the Supreme Court is "hidding behind technicalities." There may well be truth in that. But it doesn't change the fact that a critical battleground today is over who has to prove what.

This is what the NAACP's Jones is referring to when he says his side is being asked to "prove that water is wet." Given the horrible abuse of blacks going back to Jamestown in 1619, Jones believes that American society should be presumed guilty and should have to prove itself innocent. Yes, what he's suggesting, he says, is "a national burden shift."

While nobody should count on that, something else is happening that Jones calls "the most hopeful development": HEW's Office for Civil Rights is beginning to gather evidence of deliberate segregation in schools and elsewhere.

"In the past year, we've been steering OCR away from findings based purely on statistics," OCR director David Tatel says. "We have a heavier burden, and if we expect to defend these findings, we've got to convince people there's discrimination . . . Now a statistical finding will trigger a further investigation . . . You look for acts of discrimination. You look for intent . You have to be able to say that this statistical showing has something to do with discrimination."

In other words, one of Washington's aims 25 years after Brown is, in effect, to help the NAACP prove that water is wet.