In an age of fat, amorphous biographies of literary mediocrities it is good to have this lean, efficient biography of the man who may well have been the greatest English writer after Shakespeare.

Norman and Jeanne MacKenzie, authors of earlier works on H. G. Wells and the Fabians, have here tackled one of the richest, most prodigious of literary lives and brought all its complex strands together with meticulous scholarship and abundant human understanding.

They rightly see the key to Dickens' larger-than-life personality in his inordinate need to be loved - a need springing from his semi-abandonment by his feckless parents when he was 12. It was then that his father went to debtors' prison, leaving the ambitious boy consigned to pasting labels on pots of shoe-blacking in a rat-ridden wharf factory.

Everybody needs to be loved, but few have Dickens' vast resources of genius and energy to extort that love, as he did, from practically the entire world. As if his immensely popular novels were not enough, he was a tireless propagandist for the poor, an amateur but gifted actor, a philanthropist and a prodigious traveler and correspondent.

And if you were so illiterate as not to be able to read his novels, he would even read them to you, acting out each part in the famous public readings which ultimately burned him out at the age of 58.

In his personal life he sandwiched in an unhappy marriage to Kate Hogarth with an early, unsuccessful affairs with the flirtatious, empty-headed Maria Beadnell and a late, scandalous affair with the much younger Ellen Ternan, whose dark beauty inspired Dickens to deal for the first time, in his late novels, with real women.

"I have a strong spice of the Devil in me," Dickens once confessed in a letter, and to his side of their subject, too, the MacKenzies do ample justice. While he was admirably forbearing with his leech-like family, this pillar of home and hearth who abetted the ideal of Victorian domesticity blamed his wife for her perpetual pregnancies and was something of tyrant to his many, unhappy children.

When, at the first crest of his fame, he felt insufficiently loved in America - a "land of freedom and spittoons," he called it - he voyaged to lecture as on our characteristically freewheeling copyright laws, which were costing him a fortune through piracies, and he seemed genuinely surprised when his sermonizing was received with ill grace.

Another aspect of Dickens the MacKenzies emphasize is the astute, sometimes unethical businessman. Dickens was no ethereal esthete; he saw no reason why people shouldn't pay - and pay well - for the privilege of loving him.

The MacKenzies sum up his genius as "his capacity to reach out to his readers, like a great actor holding his audience across the footlights as much by the projection of his own personality as by his impersonation of the characters he plays."

This capacity ensured that of all the millions of words he penned in his frantically energetic career, there exists not one sentence that is limp, listless or stody. His sentimentality may pall, his humor may descent to the merely facetious, but more than a century after his death he is still read because of the electric vivacity of his prose.

Except in his letters. Dickens wrote so many of them that only now are they being collected in a serious, scholarly way, in the ongoing Pilgrim Edition. Yet, like his fellow novelists Jane Austen and Joseph Conrad - and unlike Henry James or D. H. Lawrence - Dickens was not one of the great letter writers.

Too many of them are rushed business notes, and it is mostly on the basis of these letters that the MacKenzies claim their book to be "the first new biography of Dickens in a generation."

This is not entirely true. Edgar Johnson's two-volume study "Charles Dickens: His Tragedy and Triumph," still the standard modern biography, may date back to 1952, but it is now available in a handy one-volume paperback condensation. And still more recent is Angus Wilson's superb 1970 "The World of Charles Dickens."

Both deal in greater depth with Dickens the artist than the MacKenzies do, and the Wilson book in particular is more poetically written - from the vantage-point of a fellow novelist. Pretending to be merely a coffee-table picture-book, it is also far more lavishly illustrated than the MacKenzies' volume.

Yet while the MacKenzies' work offers no really new insights or revelations, it suffices very nicely for any reader more converned with the facts of Dickens' life than with literary analysis of that unique art which justified him in calling himself "the Inimitable."