ROBERT LOWELL earned acclaim as a poet at the age of 29, when his "Lord Weary's Castle" won a Pulitzer Prize. This recognition came only two years after his first volume of poetry appeared, in 1944. But Mr. Lowell went on to sustain and enlarge his gift for 33 years. He did not dilute. Three years ago, when over 300 of his collected poems were published in "History," he was praised by one critic as "American's first poet." Throughout his career, others poets - T.S. Eliot, Allen Tate, Randall Jarrell - paid homage to Mr. Lowell as a craftsman who had traversed territories of feeling and expression uniquely his own.

Much of Mr. Lowell's poetry was personal. He was delighted when he thought the reader would "believe he was getting the real Robert Lowell." He told an interviewer for The Paris Review that "almost the whole problem of writing poetry is to bring it back to what you really feel, and that takes an awful lot of maneuvering . . . It's a terrible struggle, because what you really feel hasn't got the form, it's not what you can put down in a poem. And the poem you're equipped to write concerns nothing that you care very much about or have much to say on."

Despite such modesty, Mr. Lowell's poetry was able, as one critic noted, to find any number of subjects either to explore or denounce: "the Old Law, imperialism, inilitarism, capitalism, Calvinism, Authority, the Father, the 'proper Bostonians,' the rich . . ." In "Lord Weary's Castel," a poem that examines the poet's relationship to his New England roots and his own consciousness of contemporary experience, Mr. Lowell wrote:

Our fathers wrung their bread from stocks and stones

And fenced their gardens with Redman's bones;

Embarking from the Nether Land of Holland.

Pilgrims unhouseled by Geneva's night.

And here the pivoting searchlights probe to shock

The riotous glass houses built on rock.

And candles gutter by an empty altar.

And light is where the landless blodd of Cain

Is burning, burning the unburied grai.

If Mr. Lowell's beliefs and convictions were revealed in his poetry, he asserted them also as a citizen. A conscientious objector who served five months in prison in 1943, he was an early critic of the Johnson administration's Vietnam policies. His rejection of a White House invitation for an arts festival in 1965 was a rallying point for what was then a growing antiwar protest. If he won notoriety for his stance against the war, it was only part of a larger prominence based on the breadth and genius of his poetry. Much of it is sure to be lasting.