The Secret Museum: PORNOGRAPHY IN MODERN CULTURE by Walter Kendrick (Viking: $18.95; 265 pp.) : The Question of Pornography: RESEARCH FINDINGS AND POLICY IMPLICATIONS by Edward Donnerstein, Daniel Linz and Steven Penrod (Free Press: $22.95; 267 pp.)

Psst, feelthy uncertainties. The Walter Kendrick book is a deft history of pornography, from the last days of Pompeii to the later days of Henry Miller to latest days of a 1986 report to the U.S. attorney general--tracking the literally indefinable nature of the subject, including the classic 1964 response of Supreme Court Justice Potter Stewart: “I know it when I see it.”

The Edward Donnerstein and company book is a social sciences exploration of whether certain strains of pornography, however defined, cause its consumers to act aggressively, especially toward women--testing people in laboratory sessions that may not replicate the outside world.

Both books tend toward necessarily tentative conclusions. Both books suggest a significant change of perspective toward a traditionally dirty subject. Society--or those within society who would profess to know best about what is suitable for public exposure--used to worry about the invisible effects of pornography, earlier called obscenity, on the reader or watcher. In England, in fact, the guardians of morality were for centuries most concerned about the Young Person who happened on such materials; the prototype for the Young Person was female, frail and probably not well-educated. Nowadays, the Young Person is male, muscular and still not well-educated. The old danger centered around personal corruption. The present danger is corruption that may impel quite visible behavior, including aggressive violence against women.

Kendrick says we have entered the “post-pornographic era,” well beyond the time when lawyers and writers and public guardians argued about such delicate shadings as “redeeming social interest” or “artistic merit” or “community values.” There are materials in the modern marketplace that do not claim to be of more than prurient interest.

But the vilification of such materials now comes most angrily from red-faced women rather than blue-nosed men. Feminists, in print and in court, argue that pornography is all about the degradation of women, a “graphic sexually explicit subordination” that may incite physical attack as well as social humiliation.

The Donnerstein, Linz and Penrod study looks at that charge and offers some support for it. Having divided the indefinable into non-violent and violent categories, the three professors concluded, “on the basis of what we know so far, we have to assert that the kind of film that is most dangerous would be that which depicts sexual violence against women,” going on to suggest that such portrayals might indeed influence the behavior of “young male adolescents.”

Donnerstein, a UC Santa Barbara professor, was an important witness for the Meese Commission; his book, however, offers more cautious advice than the attorney general’s commission did. While the professors agree that pornography desensitizes its viewers and that women are demeaned as objects in pornographic materials, the three social scientists would attempt to correct the problem by programs of public education rather than by punishment for the pornographer. They question, in fact, whether the traditional fear of pornography--its erotic quotient--is as dangerous as its violent elements.

As literature, “The Question of Pornography” leaves some liveliness to be desired. So careful are the authors that they describe their methodology twice, once in the preface and again in the first chapter--delivering that old academic one-two punch of explaining what will be explained, then hauling the reader through a variety of experiments conducted with college students who had to sit through hours of pornographic films and still pictures. Some experiments cause students to be aroused. Some will cause readers to have drowsed.

Kendrick, by contrast, is a droll entertainment on a supposedly dirty subject. He takes us through the legal thicket of democracies trying to proscribe against filth while preserving free expression, including the English furor over “The Well of Loneliness,” the crusading 19th-Century prudery of American Anthony Comstock and the trials of “Ulysses,” a 1930s milestone for James Joyce.

Both volumes have value: Donnerstein for researchers who need testing data, Kendrick for readers who can appreciate the need to understand what cannot be defined.

Neither, however, grapples conclusively with the form of delivery, pornography or not. Books, for instance, remain a relatively rarefied taste. A novel of 1986, “Gerald’s Party” by Robert Coover, was juicier than Joyce but inspired no national burnings or bannings because society, including those who would know best for us on the Meese panel, has come to recognize book readers as generally nonviolent citizens--and as a harmless minority. The attorney general’s commission and other such bodies focus on films and magazines, mass-distributed products available to almost any Young Person; the images are accessible and the impact can be immediate. Marshall McLuhan may have been wrong after all; the medium is not necessarily the message, but the medium may control the potency of the message and determine its potential audience--and some audiences, such as children, may indeed need more societal concern than others.

There is a lovely literary irony here: While books, above all other forms, were making the world safe for pornography, books lost audiences in the process.