IF THE VICTORIAN custom of subtitled novels still prevailed, Jonathan Raban's near-perfect fictional debut would carry the addendum: "Or, The Thinking Man's Mid-Life Crisis."

Sixty-year-old Englishman George Grey has gone to pot in the colonies. A frustrated Navy man since his World War II service, he drifted into the bunkering business -- refueling and provisioning merchant ships -- in the Portuguese possession of Montedor, located, as he puts it, "on the bulge of Africa, one block down from Senegal."

Thanks to "agrarian reformers," Montedor has also gone to pot: spray-painted Marxist slogans adorn the statues of Portuguese noblemen, the Lisbonian balconies are falling off the abandoned houses, and George's bosom friend, the new "Minister of Communication," who once drove a cab in Milwaukee during his exchange-student days in America, spends his time playing squash in what is left of the Bom Porto Yacht Club while the telephones give off a "transcontinental crackle" during calls from more than three streets away. Post-revolutionary Montedor's only magnificence is its postage stamp, which features "a flag with some gaudy Third World heraldry on it, a sword, a fishing boat, a torch, and some sort of tree."

Knowing another revolution is imminent, the Minister sends George home with a farewell gift of a Swiss bank account containing $43,000 stolen from the Portuguese. As tactful as he is law abiding, George pretends to accept the gift and returns to an England he has not lived in for two decades.

The first unexpected modern horror he must cope with is his feminist-author daughter Sheila, the most bloodless female ideologue since Madame de Farge, whose bestselling tome The Noblest Station: A Study of Female Submission in Western Culture, is "mined with the word 'patriarchal'" and manages to find a connection between the preference for condoms by 76 percent of married couples in the London Borough of Tower Hamlets and Congreve's The Way of the World.

WORSE THAN Sheila is London itself. Raban, whose essay collection Soft City was hailed as a powerful articulation of the refined tortures of urban living, surpasses himelf here in an almost unbearable description of George's ride with a misanthropic London cabbie whose conversation is "a rain of bored obscenity . . . . The man was as inexorable as God's wrath . . . as if his anger supplied the motive power for the taxi: fuelled with expletives, it dodged, braked, slewed, cut in. With every gear change there was another burst of filth from the driver."

Shaken by the changes in London, George flees to a seaside cottage, only to meet another nemesis in Diana Pym, formerly "Julie Midnight," a '60s rock singer whose shtick was making herself up to look dead. Now an aging chainsmoker afflicted with free-floating panic, she seems to George ''all bone and nerve like a trapped bird against a windowpane." His aversion to her mounts when she shows him her garden and explains that she prefers to grow weeds: ''She liked plants that were poisonous, or crept along the ground, or wrapped themselves round dead trees."

Already on the coast, he now has no other escape but his first love, the sea. He finds a small secondhand yacht for sale at a price that tempts him to dip into his Swiss bank account; his resistance lowered by the culture shocks he has sustained, he goes to Geneva and withdraws the money.

He begins taking short boat trips that get longer and longer as, liberated by the water, he lets himself remember the people he permitted to dominate his life: his high-church Anglican priest father and his princessy ex- wife Angela, a peaches-ancream British version of the Ali McGraw character in Goodbye, Columbus, who did not want to be a navy wife.

Swamped by memories and growing ever more obsessed with the process of self-analysis, his moment of truth comes when, accused by officious bureaucrats of smuggling dope and immigrants, he decides to set sail for Montedor.

Jonathan Raban's achievements in this novel are nothing short of awesome. He uses the Noble Savage and Mid-Life Crisis themes without once letting them use him, and deftly overturns every clich,e he places in his own path. His story is packed with typical English eccentrics found in every Agatha Christie yarn, while Sheila's live-in lover Tom is straight out of those Mary Webb pastoral idylls in which ponderous working men go around saying "Eee, by goom, thart's summat," but Raban lies in wait until he finds the perfect word or deed that will illuminate them in all their hideous individuality. And incredibly, he even avoids the pitfalls of that standard scene, the Englishman's visit to a French prostitute, by making it explode in comic horror precisely while the reader is thinking "He'll never get out of this one."

The author's only fault is a tendency to strive too hard for pear-shaped metaphors. "George felt self-consciousness thicken in him like a muddy sediment in his veins and arteries" and "the bronchial voice sounded like the chinking of dead leaves in a breeze" are adventures in overkill, but happily they are rare.

His stylistic forte is the quick, seamless flashback. Dispensing with heavy signals such as linespaces, chapter breaks, and asterisks, he can dash off a twelve-cylinder Proustian reminiscence that I can only call "zero to madeleine in sixty seconds."