A PROMINENT BRITISH politician once said to me that there were probably 100 men and women in the House of Commons who would make excellent prime ministers, possibly 10,000 in the nation at large who would be better still. The problem was getting there. William Pitt had no problem whatsoever in getting there indeed his career borders on the incredible. He entered Parliament at 21. He was chancellor of the exchequer at 23, prime minister at 24 and prime minister he remained, except for one short break, for the rest of his life.

He is regarded with veneration by the conservatives as founder of the 19th and 20th-century party -- the statesman who finally brought back Toryism to respectability. It is, however, doubtful whether he ever thought of himself as anything but a Whig. Whigs as well as Tories can, therefore, revere him and do. The Whigs see him as an administrative genius who raised the armies, navies and subsides that ensured the defeat of Napoleon. In spite of repeated losses, mutinies and desperate food shortages that brought the specter of starvation to Britain, he remained calm, convinced of his country's ultimate victory. He became a legend, "the pilot who weathered the storm."

The official picture of Pitt has it slight blemishes: the savage Combination Acts which destroyed incipient trade unionism; the ferocious attacks on the very mild, pro-French radicals; the suppression of habeas corpus , the bulwark of British liberty, all may be condemned as excessively repressive. But, it can be argued, Britain was at war, in desperate danger; and Pitt's apologist point to his support of parliamentary reform, his stand against the slave trade, as demonstrating what Pitt really wanted had at times been propitious. And he is contrasted with the wayward Charles James Fox -- that erratic genius who supported all radical causes, spoke with brilliant eloquence and stumbled grotesquely in his pursuit of political power. Pitt kept him in opposition, discredited and defeated, for the best part of a lifetime. Many feel that Pitt was the realist who knew how to cope with idealistic radical cranks.

No one can deny Pitt's success. It is there. True, his administrative reforms proved meager, his economic policy was of little effect, Napoleon's defeat was largely self-inflicted. Even so, at Pitt's death in 1805, England was richer and mightier that when Pitt took office in 1783. She had become the greatest imperial power since Rome. Although his critics could rightly claim that the Treaty of Union with Ireland bedeviled Anglo-Irish politics for over 100 years and had abysmal results, it is difficult to envisage an alternative solution in 1801. Indeed Pitt's apologists have little diffculty in pressing the image of a very great man, one of the greatest statesmen who has ever resided at 10 Downing Street.

And yet, I suspect Fox would have done better, that there may have been a score of men and women in the House of Commons in the 1790s who would have done as well, because when one looks at Pitt, the man, rather that Pitt, the prime minister, one is amazed by his weaknesses and shortcomings. The great virtue of this new biography by Robin Reilly is that William Pitt's character is judiciously and carefully analyzed, and this makes the book worthwhile -- for, otherwise, it tells a well-known tale at a rather superficial level.

There was a great deal of madness in the Pitt family. His father, the great Chatham, had suffered periodic bouts of nervous breakdown; his aunts, uncles, cousins had been riddled with mental instability, or worse. Indeed as prime minister he was greatly embarrassed by the homicidal antics of his cousin, Lord Camelford, the titular head of the family. And, in this sense, William Pitt was a part of the family: never mad, true, nor as neurotic as to be incapable of business, although at times he looked as if he might be. He was inescapably a Pitt.

As Nollekens' marvelous bust makes clear, he was exceptionally arrogant and aloof, totally incapable of the masculine bonhomie which is such a necessary part of day-to-day politics. His judgment of men was based on ignorance for he was hardly interested in anyone but himself. Indeed, apart from a few members of his family when young, and a clutch of handsome young men of inferior abilities as he grew older, he found personal relationships exceedingly difficult. His arrogance was combined with intense reserve, an inner tension, presumably, from his emotional responses.

At an early age he became an alcoholic; by the late 1790s, at the most difficult moments of his premiership, he was a chronic alcoholic, often seeing double as he entered the Commons. But, like many alcoholics, he was rarely totally incapable, only very impaired. The alcoholism was due partly to the idiocy of his doctor, who prescribed port for his physical weakness as a boy. This was the experimental age of port when the amount of brandy it was laced with varied immensely; so, often, Pitt was drinking huge quantities of brandy rather than wine, even as an adolescent. However, his addiction to the bottle was probably also a response to his sexual frustrations. He was a non-practicing homosexual, doomed to lonely masturbation, at a time when masturbation was regarded as a chronically debilitating malady, the subject of a vast literature of horror. No wonder he needed the bottle.

With such exceptional defects of character, it would seem unlikely that many other politicians would not have made better prime ministers. Yet Pitt had one characteristic that the others lacked, a characteristic brutally portrayed by Nollekens but little stressed in this pleasantly readable biography -- utter self confidence in his abilities as a statesman and a conviction that lay at the core of his being that he was destined to guide the future of his country, that supreme power was his natural destiny. Endurance was the quality that bore him on and on, drunk or sober, through disaster after disaster that might have destroyed abler, soberer, more normal but less confident men.