TWENTIETH-CENTURY American poetry is a study in diversity of style and voice, but beneath the long and short poems, rimed or open stanzas, mythological densities and simple lyrics, a shared conviction gathers together much of it as the collective voice of protest against life in the modern city. No other art form has so opposed the national will to improve life by technology and urban planning. Early in the century, Ezra Pound struck the note of discord in poetry when he began dissecting the city as a vortex of mechanistic ideals, in which usury and commerce were bulwarks against an alternative order Pound discerned in pagan myths, the Greek world-view, in the lusty gods of nature, Dionysus and Aphrodite. "Learn from the green world," he exhorted.

Ever since Pound, poets have felt pressed to try every means available to show their affinities with the natural order, and to do this in the poem by presenting spontaneous modes of thought and expression, by disrupting logic with digressions of memory, emotional outburst, notation of surroundings, and myriad clusterings of unfettered association. Experiment with the medium may have diminished the potential audience for poetry, but the tinkerings with language and structure go along with the vision behind it -- to reassert that human life is in the fold of nature. At times in the century, the poem has suffered deformities from the pressure of so much experimentation, all of it committed with the high seriousness of a cause -- to regain the freedoms of a distant past, when life was viewed not as a mechanical function but as a phenomenon of mysterious moment in the vast cycles of death and renewal.

In the work of Paul Blackburn (1926- 1971), collected for the first time in Edith Jarolim's fine edition, speech is refined to an effortless fluidity, in which a few short phrases constitute a lyric. But each phrase has in it the barb of an understanding, some little beauty of nuance or perception that subtly earns approval. But ever so subtly, as in this apercu from ''The Mirror," written in 1953:

The lazy dragon of steam issues

from manhole cover. Tires hiss

The wet streets of my city speak to

me

"Issues" calls up the sibilants that follow, particularly the "hiss" of the tires, but "streets," "city" and "speaks" all answer in echoey confirmation of that hard "s," which creates the image of a rainy night. But the "dragon of steam" is the principal figure -- issuing out of the city's underworld, the unconscious of dreams and hissing serpents, which Blackburn deftly insinuates by reference to that "manhole cover."

Blackburn's "green world" lay somewhere in the unconscious, in what is primal of human nature. His eye was always searching for some tidbit of human resistance to city monotony, ''but such accidents of fate or inner nature/ are certainly occasional," he reports in a wry goat song, "Cabras." His notational style here and throughout his large canon springs from Pound's poetry, which Blackburn began reading in his early twenties. Like William Carlos Williams, Blackburn believed in "no ideas but in things," hence these trompe l'oeil lyrics catching sight of minute particulars of nature in the mechanical city. The machine age, Blackburn thought, was merely puritanism with a new face, a grinding work ethic poised against pleasure and surprise. His poems, all 678 pages of them, are the art of detecting the life force as it seeps out of the cracks of the street, from the manhole covers clamped down on it. Even Blackburn's pitiful last days battling cancer, recorded in his journals, thrust up the opposition between primordial vitality and modern entropy; he is witty and sensuous to the end of his life, a steady apostle of Pound's vision of the old elan.

ROBERT BLY is prominent among poets for having taken up the cudgels against contending schools of verse; he particularly disliked the "Black Mountain" poets, which include Blackburn, for the sort of heady arguments they drummed into their, for him, artless verses. But there are no real differences in the vision of American poets; the only contention is with the execution of the poem. Bly puts his faith in symbolist poetry, in which the outside world is transmuted by the psychological imagination before being uttered as images. That way, the self imparts to nature the concerns, fears, desires of the human realm. Loving a Woman in Two Worlds is a series of meditations on getting older, in which he dismisses the mechanistic notion of aging as entropy and dysfunction. It is a new state of mind, a different "house" of the body, in which love reveals connections between physical and spiritual realms.

The lizard moves stiffly over November roads.

How much I am drawn toward my

parents!

I walk back

and forth, looking toward the old landing.

Night frogs give out the croak of the

planet turning.

The book is vintage work by a true craftsman; his poems are delicate formations of a few lines, held together by no more than a tone or a slight pattern of vowel sounds. There are few statements, but the change of heart brought on by the years is clearly spoken through images of twilit lakes, night birds, the comforting darkness.

Galway Kinnell's The Past takes up the same theme, but only after two sections of poems on rural life, by now a boring subject. We tag along on the poet's strolls, his chores around the farm, his bucolic musings; the natural ideal is thus made tangible, but not interesting. But in section three, the theme of memory and longing places youth in a garden, the natural realm, which again makes the green world a mysterious, sought-for alternative to modern life. "The Seekonk Woods" is a brilliant masterpiece on the subject of aging, in which a railroad track becomes a metaphor of mechanistic drudgery against impulsive life. In youth, its ties were "too long" for his stride, and in middle life "too short." Kinnell speaks for his gifted generation when he closes thus:

Behind,

the world made of wishes goes dark.

Ahead,

is not tomorrow then never, shines

only what is.

Dave Smith is writing at the head of his own generation; at 43, one would think he had few losses to ponder, but his considerable output (eight books to date) from which The Roundhouse Voices is a selection, makes a relentless lamentation over lost innocence. Many poems turn on an event in which he was lured through sexual encounter into the world of adults, parenthood, family, and thus the sorrows of generation and death. Smith's world is one of decaying boats, disappearing towns, deceased relatives and old friends, with few consolations in the here and now. His nearly operatic lushness can sometimes make one feel he is raising more than this one complaint; second readings show him to be an obsessive chronicler of youth crucified by wily country girls. It does not give him much to savor, though he writes volubly of his dilemma. In a poem on parenthood, he imagines a dignified suicide:

All I want is to stand at the top of the

stairs

once more, the hall light yellowing

the foreheads of those I love,

letting my voice be in their dreams,

saying softly, Goodbye. Goodbye.

Smith is deeply troubled over sexuality, and in many poems associates the female with knives, scissors, weapons of all sorts, which he suspects are implements used to bring boys into manhood. This is narrow experience, but it is never monotonous; the sheer powers of Smith's language, his musical lushness, the complex punning -- at which he is a master -- are all so heaped upon his arguments that one falls under his potent spells and believes what he says. He has a gospel, but it isn't the old familiar one, or is it?