That scholarly, witty and enthusiastic medievalist, Mr. T.H. White, has produced a third fine book devoted to the Arthurian legends. Sir Lancelot of the Lake, the "Chevalier Mal Fet," is the central figure; and the darkly mystic, thwarted character which Mr. White finds him to be dominates the book. Hence "The Ill-Made Knight" is a more thoughtful, adult and subdued piece of writing than "The Sword in the Stone" or "The Witch in the Wood." It has its fits of farce and comedy -- its irreverent poking of fun at some of the solemnities of the days of chivalry -- but not the out-and-out joyful boisterousness of the earlier volumes. It does a fine inside job of its study of Lancelot and of the cycle of the Round Table's history, viewing them from the vantage of modern standards. "The Ill-Made Knight" is a better book than "The Witch in the Wood." It ranks with "The Sword in the Stone," but is a different sort of book, more mystical than magical, more a novel than a prime fairy story.

The tone here has something of the spirit of debunking. Mr. White (who has an intimate acquaintance with Malory) shows what he considers the true Lancelot, Arthur, Guenever and the others, without the romantic trappings of [Lord Tennyson's] heroes.

Lancelot, Arthur and Guenever, who all loved one another, are pictured in an eternal triangle that would baffle the efforts of a 1940 psychoanalyst. But the author doesn't handle it so. He tells in simple language of the aspirations, loves and loyalties of fallible yet decent people. He makes these well-known figures seem real human beings facing stupendous problems.

They are not, however, stewing in their own juices all the time. Comic adventure raises its merry head frequently. Lancelot met the young Elaine when he rescued her, pink and naked, from a cruel and ridiculous enchantment which had held her captive for years in a bath of boiling water. And the blistering comments on the sanctified Galahad by his comrades in arms supply an ironic picture of how the completely holy must ever appear to the less saintly.

On the other hand, there is a good deal of random killing, with some uncomfortably realistic details of the bludgeoning and butchering that went on in tournaments. Lancelot himself was so frequently hacked up that this reader was surprised he survived the last page.

The most moving and beautifully told episode in the book is the account of how Lancelot achieved his heart's desire when he was prepared for the ultimate humiliation.

A great part of the story's charm, as in its predecessors, is the rich background of medieval lore -- odd bits of information, long lists of heraldic terms, a lovely collection of items in one course of a meal -- rhythmic and resounding words that impart their medieval color even though the reader doesn't know exactly what they all mean. Details of weight and construction of armor -- or of Guenever's bathroom in the castle -- are illuminating and interesting.

For one reason or another you are bound to find this new story of an old hero an absorbing and inspiriting tale. More power to the White Knight.