EDWARD THOMAS (1878-1917) has long been considered among the best of the English poets killed in World War I. Unfortunately, the label "Georgian" has been stuck to these young men, damning them with its associations of effusive sentimentality and keepsake-album lyricism.

In fact, Thomas was a tough-minded critic and reviewer long before he became a poet. He was for most of his life a hack--albeit as gifted a one as the age could offer. He reviewed reissues of the Engl, ish classics, slim volumes by new poets (among them, Walter de la Mare, D.H. Lawrence and Ezra Pound), books of natural history, and whatever else he was sent from the Morning Post or Daily Chronicle. Edna Longley, selecting from Thomas' million or so words of reviewing, has presented the best of his prose in this attractive volume.

Reading straight through A Language Not To Be Betrayed can be, however, somewhat deadening--like Poe, another prolific reviewer, Thomas didn't always have first-rate work to criticize. Still, what is here is fine-- straightforward sentences, sly plays of wit, and uncomfortably up-to-date pronouncements. Who, for instance, does not recognize this kind of critic: "We are left to wonder why he is interested in literature, except in so far as it gives him an opportunity of showing the world that he is, as we say, a clever man."

At times Thomas can be as cutting as Randall Jarrell at his meanest: "We are inclined to think, moreover, that the only poet who was ever popular is Longfellow, and even that exception depends upon the admission that he was a poet." And, again like Jarrell, he can capture a writer's flavor in a phrase: Burns' love poems "are a superb expression with a few variations, of what a man of simple and hearty nature, full of blood, feels at the sight of a woman worthy to awaken his desire." He can be quietly right too. "That love poetry seems so often to have little to do with love is because we forget that there are matters in the presence of which any man and Shakespeare are equally impotent and silent."

Who could not like such a writer? Thomas' slightest work reveals an appealing human being, as well as a critic with style and acumen. And courage. Reviewing the first book by an unknown American he proclaimed it unflinchingly: "This is one of the most revolutionary books of modern times, but one of the quietest and least agressive. It speaks, and it is poetry." The collection was North of Boston, by Robert Frost.