Tom Sharpe! Tom Sharpe is here!; Wilt, by Tom Sharpe. New York: Vintage Books. 221pp. $3.95 The Throwback, by Tom Sharpe. New York: Vintage Books. 223 pp. $3.95 Vintage Stuff, by Tom Sharpe. New York: Vintage Books. 223 pp. $3.95

IT has been said that a novelist's first duty is to entertain, and Tom Sharpe - a very popular British novelist whose work is at long last available in this country - performs that task with obvious devotion. He's a desperately funny writer.

But there's nothing quiet about Sharpe's desperation. Something has driven him to the very boundaries of good taste in vocabulary and fictional event. His fiction is by turns ribald, farcical, satiric, silly, raucous, preposterous, political, irreverent, and wonderful - it succeeds through excess, suggesting a coarser Evelyn Waugh or P.G. Wodehouse leavened by Monty Python.

''Wilt'' (1976) is the best of the three Sharpe novels just published in paperback original in the United States (the others are ''The Throwback,'' and ''Vintage Stuff''). It is an academic novel and considerably more humorous than Kingsley Amis's ''Lucky Jim'' or Malcolm Bradbury's ''The History Man,'' the two most consistently praised British books in this genre.

Sharpe's protagonist, Henry Wilt, teaches at Fenland College of Arts and Technology. He is a lecturer (Grade 2) in liberal studies who has, he says, spent 10 years ''going from classroom to classroom with two dozen copies of 'Sons and Lovers' or Orwell's 'Essays,' or 'The Lord of the Flies' '' in an effort to ''extend the sensibilities of Day-Release Apprentices with notable lack of success.''

After all this time teaching Meat One (Butchers) and Gasfitters Two, Wilt says he has developed a ''phobic reaction'' to ''The Lord of the Flies,'' and is , in every conceivable respect, at the end of his tether. He decides to murder his wife, Eva.

Eva Wilt is the sort of woman who ''hurled herself into cultural activities and self-improvement with an enthusiasm that tormented Wilt.'' Describing her, Wilt asks, ''You remember that series of Garbo pictures they showed on TV some years back? Well, Eva was La Dame Aux Camelias for three days after that. . . .''

Not the most assertive of men, Wilt decides on a trial run. He will commit symbolic murder first, by doing in an inflatable doll that has come into his possession by circumstances so improbable and offensive as to have caused Eva to leave home unannounced, whereabouts unknown, with a hopelessly pseudo-progressive American couple, the Pringsheims.

Wilt decides to stuff the doll, dressed in Eva's wig and clothes, into a deep hole at a construction site just outside Fenland's classroom building. Soon after, as concrete is poured down the hole, one of the workers spots the doll and thinks it is a real woman.

Wilt soon lands in custody, his wife is nowhere to be found, and an extremely funny interrogation which occupies a good third of the novel begins. Told to start at the beginning, Wilt says, ''God made heaven and earth and all . . .'' The innocent-in-deed-if-not-in-wish Wilt proceeds to drive the police, especially one Inspector Flint, crazy.

At Fenland, they miss Wilt. ''Wilt's absence,'' writes Sharpe, ''was making itself felt in more ways than one. Mr. Morris has had to take Gasfitters One at 9 o'clock and had come out an hour later feeling that he had gained fresh insight into Wilt's sudden excursion into homicide.''

Passages of this sort are everywhere in ''Wilt,'' passages of classically British understatement, but it would not do to call Sharpe subtle. Both ''The Throwback'' (1978) and ''Vintage Stuff'' (1982) are farces in extremis in which events explode out of control.

Lockhart Flawse, the central character of ''The Throwback,'' is in the tradition of Fielding's ''Tom Jones'' and Edgar Rice Burroughs's ''Tarzan'': a primitive who collides repeatedly with ''civilization'' (so-called) with comic results.

Here is Flawse learning to drive: ''More accustomed to the ways of horses and buggies than to the sudden surges and stops of motor cars, Lockhart's driving consisted of putting his foot flat down on the accelerator before letting out the clutch and then putting his foot flat down on the brake before smashing into whatever stood in his path.'' The above also approximates an allegory for Flawse's approach to life as lived in the 20th century.

''Vintage Stuff'' features Peregrine Clyde-Brown, a boy who takes everything literally, and one Mr. Glodstone, Peregrine's master at a third-rate private school. Together they enact a boy's adventure story, in unbelievable paramilitary fashion and gone horribly wrong, in France.

The excesses of Sharpe's novels are deliberate - Sharpe is a careful writer and a meticulous plotter - and even if the cumulative effect is something like a Monty Python sketch, Sharpe does make his points. Like all good humorists, he is serious and his observations are disturbingly close to the truth. Irreverent to the last, Sharpe's brand of no-holds-barred satire and farce is the funniest stuff I've read in years. Start with ''Wilt.''