On this side of the Atlantic, Renata Adler is best known, if she is known, for a single act of journalism published in the New York Review of Books almost 35 years ago.

That is her misfortune, but it also does potential readers few favours. There is a much more to Adler than a controversy between Manhattan scribblers - over the epochal issue of film reviewing, no less - a generation back.

Nevertheless, one long piece, physically the centrepiece of After The Tall Timber, is as good a place as any to start for anyone new to Adler. When it appeared, the evisceration of the reputation - and the writing - of the New Yorker critic Pauline Kael caused a stir (and then some) among those who had come to treat the composition of hit-and-run film crits as an art in its own right.

For one thing, both women were working for the same magazine. For another, though Adler was expending 8,000 words reviewing a collection of reviews, the single word that stopped every clock in New York media salons, the word that endured like a sentence handed down by a hanging judge, was utterly brutal. Kael's writing - therefore her opinions, her knowledge, her long and distinguished career, by insinuation her person - was "worthless".

People were divided. Some of us, junior scribblers at morning movie previews thousands of miles away, were delighted. Kael had become eccentric, tyrannical, and - worst of all - sloppy. She made mistakes and acknowledged no errors. The former renegade had become a one-woman critical establishment. At the start of the 1980s, with her best work far behind her, she had become that hellish thing, the doyenne. She could and did make or break reputations. Adler returned the disfavour.

Yet that was not, or not exactly, her intention. Granted, she employed a good deal of the reviewer's time-honoured street-fighting skills. Above all, there was the feint-before-the-slap. So one paragraph concludes with, "I, for one, continued to believe that movie criticism was probably in quite good hands with Pauline Kael". The first sentence of the next paragraph has barely commenced before there's one, the famous one, to the kisser: the entire book is "simply, jarringly, piece by piece, line by line, and without interruption, worthless".

So what? When compared to political hacks, the culture crowd are a disputatious bunch. Their gangland feuds are unending. But none of that, I suspect, was Adler's real purpose. She was asking a question, one that recurs throughout After The Tall Timber and gives the book its Mary McCarthy-inspired title: what has become of American journalism? The assault on Kael was Adler's way of restating Orwell's belief that corrupted language and rotten editorial practices are manifestations of a deeper decay.

Such a position has need of certain techniques. Adler, born in 1938 and therefore a child of what she regards as a "middle" generation caught between the Depression, the experience of war and the 1960s, has the obvious marks of New Criticism. She is a close reader even of casual statements. She expiates on words and phrases to make larger points. She has the forensic habit and she luxuriates, in the manner of a chosen few journalists of her American generation, in the acreage allowed to her prose.

It is questionable (let's say) whether anyone could ever need 8,000 words in which to garrotte a failing critic. But at the New York Review and the New Yorker, the garrulous exposition was, as it remains, near-venerated. A lot of words are intended to convey a single word: weighty. And Adler's line readings, slowly picking apart failed sentences to reveal the failed assumptions on which they rest, invites the same Jesuitical response.

A tiny example. She nips at Kael for hyperbolic exaggeration. The charge is accurate. But among Adler's examples is the phrase "poisonously mediocre". Which test is failed? This is not a reference to harmless mediocrity, to the tediously mediocre. It is not the best combination of words ever put on paper, but it is a long way short of the worst. The objection is nitpicking.

Kael's career stands as a hideous early warning of what was to become of journalism when the internet hit. The shrill self-regard, the attention-seeking, the cult of celebrity: 35 years ago, it was all there, and all of it "influential". But pomposity allied with viciousness, in Adler's style, go back to Grub Street. It is not, or not always, exemplary because of its vintage.

All the golden ages are behind us. Adler takes apart Bob Woodward or legions of New York Times page editors in ways that are always fair - or "uninflected", as she might prefer - and always have a larger purpose than quibbling over style. Her own reporting of, for example, the murderous comedy known as the National Guard, a bunch of Vietnam draft-dodgers busily killing black Americans when she wrote her piece, is exemplary.

But she is animated, from the 1960s to the 21st century, by the idea that once things were better, standards higher, celebrity bylines fewer, and pernicious "anonymous sources" unknown. Orwell suffered the same delusion. Yet you need read only Mencken or Twain, or enjoy The Front Page, to realise that bad prose, bought hacks and establishment vanity are nothing new. The timber invoked in Adler's title was never quite as tall as disillusioned romantics like to believe.

The author's answer is implicit, nevertheless, in her own pages. She is a pleasure, often a joy, to read, precisely because she applies her principles to the material. Sometimes the pieces, like the sentences, are simply too long to sustain the nuances and qualifications that lead Adler towards her truths. Sometimes everything is justified. A "letter" first published in the New Yorker in April 1965, here retitled as "The March for Non-Violence From Selma" is still one of the best things written about the civil rights movement. It works, I think, simply because Adler walked a contested road with her eyes, ears and mind open.

Sometimes she is very funny. Her account of dealing, as a film critic, with the mandarins of the New York Times - in those good old days - is a reminder that great newspapers can become asinine bureaucracies full of people who will ruin jokes, introduce errors, and destroy a writer's confidence because, in some strange fashion, such is an editor's role in life. A piece on the intellectual decadence of the American left as the 1960s petered out meanwhile describes a meaningless motion put before a chaotic convention: "No one protested. Everyone was baffled. And it passed."

Adler's work is not a reminder of how journalism used to be, but of how good, now and then, it could be when acute minds paid attention to the words published below their names. She sensed, decades ago, an ebbing of public faith in the business of journalism and tried, by example and interrogation, to find the reasons.

Her country is a republic founded on a belief in free speech and a free press in which, as often as not, few still believe a word they read. That's worth writing well about. Adler writes very well indeed.

After The Tall Timber: Collected Nonfiction by Renata Adler is published by New York Review Books, priced £20