THE SO CALLED media critics of our day are a pale bunch, all in all, members of a parasitic trade composed of smallminded men who exaggerate their own courage. Most of them merely pick through the manure pile for peppercorns, which they hold up for mild amusement.

One longs for real critics, robust and corrosive intellects who, instead of picking at obvious nits in newspaper content, would pursue the deepest questions about the press. What lurks in the soul of American newspapers that makes them do what they do?

H. L. Mencken gave us a wonderful glimpse of the answer in his autobiographical volume, "Newspaper Days." He was a wet young kid on a bicycle, chasing fire engines to the scene of a story, then racing other kids on bicycles. The firs kid back to the newspaper got to sell the story. That is how reporting worked in 1900, and there is still a lot of bicycle-racing in the trade.

A. J. Liebling drew a deeper portrait, more analytic and more devastating. He read today's newspaper and remembered that yesterday's said something different. But neither he nor Mencken wrote with any pretense that they were somehow "reforming" newspapers. Both believed in the permanence of human silliness and in the essential hilarity of what newspapers presume to do.

Now I have ome upon another robust critic, an ex-editor who lacks the artistic skills of Liebling and Mencken but express such total contempt for the press that his wrath approaches grandeur. Lambert A. Wilmer spent 30 years as an editor and writer on various East Coast newspapers, so he speaks from his own bitter experiences.

I walked in the beaten path of our journalism," he confesses floridly, "without reflecting that it might be the broad road to infamy and predition." Yes, Wilmer committed the rankest sins of our trade. "I have recommended books which I never red, singers whom I never heard, dancers whom I never saw . . . and candidates for Congress whom I would not have employed as cooks or scullions in my kitchen." This lends an insider's authenticity to his indictment, which contains 15 counts in all. I will cite here only a sample:

I charge the American newspaper press with the tyrannical exercise of power and authority to which it has no claim . . . with practical hostility to our republican government and to all free institutions . . . with a systematic and continuous effort to mislead the judgment of the public . . . with invading the sanctuary of private life, disturbing the peace of families, giving extensive circulation ot groundless and malicious slanders. . . . "

This gives you the delicious flavor of Wilmer's book. The full title is "Our Press Gang, or, A Complete Exposition of the Corruptions and Crimes of the American Newspapers." It was published in 1860. The most entertaining chapter is the one on the flogging of editors for their various indecencies.

Beyond the obvious point -- that press criticism of 1860 sounds a lot like the complaints of 1980 -- what Wilmer's wounderful rare book offers is another window on the kind of grand question which real critics would try to address. What are the inherited reflexes that guide newspapers? Why do they behave badly now and then, so irresposibly in the eyes of some of their readers? What makes the press so powerful or, as some would say, so arrogant?

Ex-editor Wilmer had an explanation that reflected mid-19th century attitudes. He blamed foreigners, especially the Irish. Half the reporters in America, he estimated, were hot-tempered young Irishmen, lately cast upon our shores, with therabble's class resentment and insurrectionary visions still in their heads. Furthermore, 300 American newspapers were then printed in foreign languges or addressed solely to communities of unwashed immigrants. These ethnic journals espoused alien ideas from Europe, socialism and anarchy, even abolition of slavery. What this country needs, Wilmer cried out, is an american press, devoted to americanism .

In one sense, that is what the nation got. As printing technology changed, as these disparate groups of new Americans were drawn closer together and assimilated, their feisty, individual newspapers declined, replaced by the modern mass-circulation newspaper. The mass-circulation press attempts to speak to all groups, the aggregate audience, simultaneously, though every reporter, every editor inherits dim memories from that institutional past when a newspaper spoke for a singular viewpoint.

Indeed, the modern press is an approximate metaphor for sociological change in Americaln life, a status report on the melting pot. While many ethnic papers still survive, they are less crucial to their readers' lives than they once were. The two groups of citizens who probably still depend most on their minority newspapers are blacks and Hispanics, a statement by itself on their separation from the rest of us, and also on the unconvincing efforts of the mass press to include them sufficiently in the mass audience.

The mass-circulation newspaper, after all, follows an economic imperative which is not so different from other modern businesses. It asks: What is our market? It difines its content to hold the audience and, if possible, to expand it. This is quite different from the papers Wilmer denounced, and the differences between today's newspapers and the 19th century variety are expressions of marketing principles.

First, the mass press, thanks to Hearst and Pulitzer and other great publishers of the "yellow" era, invented unifying themes which would appeal to all readers. As James David Barber of Duke University has observed, the most popular and potent theme is the story of a fight, whether political of physical or even spiritual. This melodrama endures on your front page, every day, along with other familiar formats for packaging information.

Doesn't that boil down to the old cliche -- you're just printing this to sell papers? In a sense, yes, but this is honest work, if it is honestly done. If one believes that life is infinitely intresting and that newspapers should strive to convey this, then a dull paper is a king of failure too, no better than dishonesty.

Second newspapers devised what some editors call the "smorgasboard" approach -- a wild variety of content aimed at special tastes in a broad audience. This segmenting of content, from political news to recipes to racing results to obituaries to stock-market tables, may be the most important element in holding the mass audience together. If a reader ignores or even despises the front page, he may still pay his two dimes to get the sports section. He is, therefore, counted in the audience which draws in advertisers.

Finally, most newspapers modulated their voices. If you read the journals of 100 years ago, the writing was more vivid and personal, certainly more passionate. The reporters were addressing a narrower audience, composed mainly of kindred spirits, people who more or less shared the same opinions and prejudices. Newspaper prose today seems bland by comparison, cloaked in a tone which is meant to lend authority but also to avoid offending anyone. The word is homogenized, exactly what the market requires.

People do resent the press anyway, partly because it is influential, partly because they feel homogenized by its depersonalized voice, partly because papers do occasionally misbehave and violate the standards of one group or another.

In these terms, the cultural upheaval of the 1960s was actually a reactionary period, an explosion of resentments against modern organization that produced many new newspapers of the extinct variety -- the so-called "underground press" which spoke in highly singular and personalized terms to smaller audiences who already agreed on values, politics, music, whatever.

In time, the mass press learned to mimic the less controversial aspects of the "underground press," trying to catch up with some segments of the mass audience. The smart newspaper borrows values from its changeing audience, even if some members of the audience are offended by change.

Thus, I would say the reflexes of a successful newspaper are guided, on its good days, by both of these traditions -- the marketing principle and the feisty heritage of the singular voice. Marketing dominates, but there is still a little "Irish" left in most American newspapers, an occasional whiff of anarchy. The two traditions are not necessarily contradictory, though I suspect most reporters, in their misguided heart of hearts, honor the feisty tradition and scorn the idea of marketing.

The paradox about modern newspapers, which most media critics seem unable to grasp, is that the marketing principle is what makes them free -- some would say arrogant -- which allows them on occasion to offend segments of the audience to behave irresponsibly in the eyes of some readers. The mass market gives the successful newspaper a kind of free speech which the old minority newspapers never enjoyed.

When a newspaper fails the basic question -- what is our market? -- then people begin taking their dimes elsewhere. When the audience goes, fame and influence and the freedom to outrage soon follow.