OPENED GROUND

Selected Poems, 1966-1996

By Seamus Heaney

444 pages. Farrar, Straus & Giroux. $25.

SEAMUS HEANEY

By Helen Vendler

188 pages. Harvard University Press. $22.95.

Perhaps the best descriptions of Seamus Heaney's extraordinarily rich and varied oeuvre come from the poet's own work: his verse not only gleans ''the unsaid off the palpable'' but also captures the ''music of what happens,'' both in the domestic sphere and in the larger world beyond. Eschewing ideology and ''the diamond absolutes'' of partisans on both sides in Northern Ireland, Mr. Heaney has created a remarkable series of poems that stay ''true to the impact of external reality'' while at the same time remaining ''sensitive to the inner laws of the poet's being.''

Happily for the reader, the publication of ''Opened Ground,'' a new selection of Mr. Heaney's poems spanning the years 1966-1996 and demonstrating the consummate virtuosity of his work, coincides with the publication of a monograph on his verse by the Harvard professor Helen Vendler, the most astute and eloquent critic of poetry at work today.

Ms. Vendler's ''Seamus Heaney'' serves as a wonderfully succinct road map to the poet's verse, illuminating the effect that both private and public events have had on the development of his work, while explicating the continual evolution of his style. She shows us how Mr. Heaney has pushed the boundaries of the traditional lyric poem in his efforts to articulate his changing vision of the world, even as she helps us to understand his masterly use of sound, symbol, imagery and parable.

As Mr. Heaney points out in his 1995 Nobel lecture, his writing has been...