Gentle essays show gift for the unpredictable

Shards of Light: Fables, Essays, Sonnets and Humor, by Neil Millar. Cambridge, Mass.: Foursquare Press (4 Merrill Street, 02139). 189 pp. $18.95 in hardcover, Neil Millar, ''this gentle man'' as the biographical sketch at the start of ''Shards of Light'' describes him, was a writer who found ''tongues in trees, books in the running brooks, Sermonscap correct in stones, and good in everything.''

As readers of this newspaper know from his articles and essays published here over the years, not everything he wrote is in the scintillating realm of fantasy , but he seems to have been happiest there. At his best, he invented parables which are more than ingenious parallels for familiar situations; they actually arrive, often by enchantingly unexpected tactics, at surprisingly bright solutions to tired old perplexities.

Mr. Millar was deftly (and sometimes daftly) keen on verbal tricks and antics , an incorrigible punster, an epigrammatist. He tosses scaly cliches on their heads, and they grow new tails. He is rarely without a good axiom to grind (though they often acquire a novel edge, as, for example, ''What can be cured should not be endured''). It's fun if you like that sort of thing and endearingly groanworthy if you're not so sure. Either which way, you can't miss his gift for the unpredictable and his mischievous boyishness.

Among the stories, essays and poems here, some of the most delightful pieces are glimpses of his boyhood in Australia. The reluctance of the small boy faced with his first day at school; the 14-year-old studying with comical admiration his own features reflected in a window at night; the 16-year-old's reveries as he sits on his bed, learning, or sort of learning, Tennyson's ''Ulysses.'' These earlier selves are observed with candid insight and affection.