In his own way: Derek Walcott; Midsummer, Poems, by Derek Walcott. New York: Farrar, Straus & Giroux. Unpaginated. $12.50 cloth.

There is much that is praiseworthy in ''Midsummer,'' a sequence of 54 lyrics that record one year's passing in the poet's life from summer to summer. Mr. Walcott was born in the Caribbean and now divides his time between Trinidad and Boston, where he is a professor. The poems focus on the torrid stasis at the heart of summer, the poet's relationships to family and place, and the peculiar perspective of the exile. Immediately apparent is Mr. Walcott's care for language; there is an exuberance, almost a physical pleasure in the construction of his lines that invites the reader to speak the poems aloud.

Two-thirds of the book is set in either the islands of the Caribbean or the tropics of Central America; Mr. Walcott, who is also a painter, offers a wealth of visual detailing in each scene. But the enlivening spark is provided by metaphor - in fact, more metaphor-per-poem than I've come across in a long while. His comparisons are ingenious, wry, bitter, and often provocative.

But I would say the poet's strongest quality is his finely tuned ear and musical sense. Mr. Walcott's composition is essentially musical, and his long free verse lines overflow with slant rhyme, half rhyme, assonance, and alliterative designs. The rhythmical structures and sound patterns propel the reader through each piece with the effortlessness of song and provide a cohesion to the poem's development.

Duly impressed by the technical strength of Mr. Walcott's writing, I found it hard to understand why, in the end, ''Midsummer'' was such a disappointing book. One quality the poet is in short supply of is balance, a sense of proportion that can sustain a tension within the writing and put his strong qualities to their best use. After a time, we are so awash in sparkling language and intricate metaphor, the subject of the poem is all but obscured. We begin to long for the simple declarative line, for unembellished description that holds clear and true. As with the dazzling midsummer sun that fills so many of these poems, we soon become accustomed to its brightness and weary of the sweltering word-choked atmosphere. At one point, the poet himself laments: ''Ah, to have/ a tone colloquial and stiff,/ the brevity of that short syllable, God,/ all synthesis in one heraldic stroke,/ like Li Po or a Chinese laundry mark!'' Yet even in his envy, he persists in his own brand of self-conscious eloquence.

The real problems begin once you look beyond the brilliance of the oratory; you are surprised by the thinness of the conversation the poet is offering and his acutely myopic vision. The lines rarely carry you further than an arm's length from the poet himself. Too many times the reality of the subject is effaced by the choice of a word or phrase that merely satisfied the cadence or figure of the poem. You are left justifiably suspicious, wondering where the writer's primary commitment lies.

Once you've finished the book, you realize that, despite the progression from one summer to the next, there is surprisingly little sense of movement or development in either time or character. The settings shift dramatically, from the Caribbean islands to Boston and New York, with side-excursions to Great Britain and Central America. Yet there is hardly the feeling of motion and only the barest sense of place. We never come to 'know' Mr. Walcott's territories the way we are given Williams's Paterson, Donald Hall's New England, or James Wright's Midwest. The many landscapes begin to feel like colorful backdrops for what we soon realize is the true subject of ''Midsummer'': the mind of the poet.

What we have is one more portentous self-portrait of the poet-at-work - a curious sensibility more at home in the world of words than in any country, more anxious to articulate his psychological responses than any experience he and the reader might have in common. This is the dead-end street in which so many of our contemporary poets have found themselves stranded: language as a performance medium for the all-devouring self, places mere occasions for the exercise of the imagination.

In one characteristic, then, Mr. Walcott is indeed representative of a broad and particularly modern viewpoint, but not necessarily one our society can be proud of. This is the role of poet-as-tourist, the outsider gliding over but not through settings, whose literary concerns outstrip his emotional involvement. This need not have been the case considering the subjects the poet has chosen for himself: the universal significance of the seasons, the racial conflict in America, the confrontation between politics and history in Central America. But curiously we find the head engaged but the heart left in neutral. The image that came to mind was that of a 20th-century Baudelaire, a super-subjective narrator of a society in decline. But ''Midsummer'' is too careful and self-possessed to incite a revolution of the spirit, and never achieves the daring and power required to truly expose the outer or inner worlds. Instead we are left with a scrapbook of color snapshots, dramatic but two dimensional, in which too often the figure of the poet is obstructing the view.

Another current runs just beneath the surface in ''Midsummer,'' the poet's personal speculations at having reached the solstice of his life and career. The poems are rife with uncertainty about the value of his writing. ''What if the lines I cast bulge into a book/ that has caught nothing?'' There is a handful of poems in the sequence that ought to soothe his doubts; remembrances of his boyhood in the islands, an apocalyptic vision in Chicago, and several selections from the ''Tropic Zone'' section are substantial exceptions to the book's ruling hypersubjectivity. For me, Mr. Walcott is so splendid a stylist and so talented a craftsman, I can only look forward to a subject that will draw him in this way out from the smothering self-consciousness and give him room for a broader, more vital creation.