What makes poetry poetic? -- two critics' views; Part of Nature, Part of Us, By Helen Vendler. Cambridge: Harvard University Press. $15.; Lives of the Modern Poets, by William M. Pritchard. New York: Oxford University Press. $14.95.

Modern poets can be placed, for handy reference, into two categories: the Putters-In and the Leavers-Out. Putters-In believe that the world can be caught in the net of words. Take the case of Frank O'Hara, who sought to "synthesize all of the American experience" with his "tumultuous vocabulary":

"Chasubles and buzz saws, zebras and tendrils, yawns and ponies, gullies and rattletraps, Afghanistan and Broadway, Prussian leather and Mack trucks, the US Senate and Spenser's False Florimell -- all join the proliferating herbage of O'Hara's acquisitive mind." (Vendler)

Or take the case, slightly different, of Allen Ginsberg, who "has bought a farm" (1969), and "lives there in a tragicomic mixture of live animals, killed animals, cows who eat his Blakean sunflowers, batteries that fail, detergent-fouled creeks, the Pleiades, the day's radio news, memories of the dead, books, rain, returnable Ginger Ale bottles, quarrels, abashed recollections of Marie Antoinette playing milkmaid, bugs on the potatoes, thoughts of Ezekiel and the F.B.I., Indian Summer, and the New York Times." (Vendler)

Helen Vendler is particularly sympathetic to these Putters-In among the poets. She admires the last poems of Robert Lowell, when, abandoning traditional forms, he wrote with a "disarming openness, exposing shame and uncertainty." She prizes his "journal keeping" even though Lowell himself despaired that he had become "only an American daguerreotypist": Sometimes everything I write with the threadbare art of my eye seems a snapshot, lurid, rapid, garish, grouped, heightened from life, yet paralyzed by fact.

Impulse to get it all into poetry, to recapture what the Victorian poets had surrendered to essays and novels, is what Vendler sees as the real work of modern poets. "From bibelots to Beatrice, from embroidery to altarpiece goes the scale," she writes of James Merrill, "and Merrill's tone modulates with its object." "What Merrill once said of Eugenio Montale -- that his emotional refinement is 'surprisingly permeable by quite ordinary objects: ladles, hens, pianos, half- read letters' -- is true of Merrill himself . . . a mark of the democratic sense in every modern poet of quality."

Turning from Helen Vendler's collected essays and reviews with their Whitmanesque democratization of poetry, to William Pritchard's Johnsonian strictures in "Lives of the Modern Poets" is like turning from the hectic heat of the city to the cool seclusion of the country. Pritchard is a traditionalist , who likes to chat with his poets, to listen to them, to read and reread, overhearing their implied, unstated meanings.

Pritchard admires the great Leavers-Out, E. A. Robinson, for example: Pritchard praises "Robinson's reticence, his solipsism even, . . . gestures of uncertainty, of how-can-we- say-for-sure-since-we-know-so-little."

Robinson's is the kind of poetry that, in his own words, "tells the more the more it is not told."

Another of Pritchard's great omitters would be Thomas Hardy. Pritchard cites the speechless speaking of "The Going," a poem about Hardy's wife's dying: Well, well! All's past amend, Unchangeable. It must go. I seem but a dead man held on end To sink down soon. . . . O you could not know That such swift fleeing No soul foreseeing -- Not even I -- would undo me so!

Pritchard comments: "'All's past amend,' and 'It must go' -- two desperate gestures at saying eternal commonplaces, the saying of which gives little help; the ellipsis after 'soon,' so passionately negative as so often in Hardy: 'O you could not know. . . . No soul foreseeing -- /Not even I -- .'"

Clearly what Pritchard approves is what is left out, what is in fact unsayable between a husband and wife, when words fail and emotion takes over. And Pritchard quotes with assent the words of Robert Frost, another of the great Leavers- Out, "Something has to be kept back for pressure."

The art of keeping back for pressure is little practiced nowadays, though Frost suggested that "for a beginning it might as well be the poet's friends, wife, children, and self. . . . We shall be judged finally by the delicacy of our feeling of where to stop."

Where to stop is relative thing. What to put in and what to leave out are the great decisions of taste. If you want two critics from the opposite ends of the spectrum of modern taste, try Vendler and Pritchard. Both know delicacy of feeling; both are astute readers, but they are as far from agreement on what makes a poem poetic as are the twinned stars of 19th-century America -- Walt Whitman and Emily Dickinson.