THE ACCIDENTAL TOURIST. By Anne Tyler. Knopf. 355 pp. $16.95.

WITH EACH new novel -- The Accidental Tourist makes 10 -- it becomes ever more clear that the fiction of Anne Tyler is something both unique and extraordinary in contemporary American literature. Unique, quite literally: there is no other writer whose work sounds like Tyler's, and Tyler sounds like no one except herself. Extraordinary, too: not merely for the quietly dazzling quality of her writing and the abidingly sympathetic nature of her characters, but also for her calm indifference to prevailing literary fashion and her deep conviction that it is the work, not the person who writes it, that matters. Of The Accidental Tourist one thing can be said with absolute certainty: it matters.

It is a beautiful, incandescent, heartbreaking, exhilarating book. A strong undercurrent of sorrow runs through it, yet it contains comic scenes -- one involving a dog, a cat and a clothes dryer, another a Thanksgiving turkey, yet another a Christmas dinner -- that explode with joy. It is preoccupied with questions of family, as indeed all of Tyler's more recent fiction is, but there is not an ounce of sentimentality to be found in what it says about how families stick together or fall apart. There's magic in it, and some of its characters have winning eccentricities, yet more than any of Tyler's previous books it is rooted firmly, securely, insistently in the real world.

That world is of course Baltimore, which in Tyler's fiction, as indeed in actuality, is both a place and a state of mind. By now Baltimore belongs to Tyler in the same way that Asheville belongs to Thomas Wolfe, Chicago to James T. Farrell, Memphis to Peter Taylor, Albany to William Kennedy; like these writers, she at once gives us the city as it really exists and redefines it through the realm of the imagination. When the protagonist of The Accidental Tourist, Macon Leary, drives along North Charles Street, he is on the map; when he arrives at Singleton Street, he is in uncharted territory. But there can be no question that Singleton Street, though fictitious, is real:

"He was beginning to feel easier here. Singleton Street still unnerved him with its poverty and its ugliness, but it no longer seemed so dangerous. He saw that the hoodlums in front of the Cheery Moments Carry-Out were pathetically young and shabby -- their lips chapped, their sparse whiskers ineptly shaved, an uncertain, unformed look around their eyes. He saw that once the men had gone to work, the women emerged full of good intentions and swept their front walks, picked up the beer cans and potato chip bags, even rolled back their coat sleeves and scrubbed their stoops on the coldest days of the year. Children raced past like so many scraps of paper blowing in the wind -- mittens mismatched, noses running -- and some woman would brace herself on her broom to call, 'You there! I see you! Don't think I don't know you're skipping school!' For this street was always backsliding, Macon saw, always falling behind, but was caught just in time by these women with their carrying voices and their pushy jaws."

Singleton Street is not Macon's natural territory. Though by no means wealthy, he belongs to that part of Baltimore north of downtown where houses are detached, have yards, are shaded by trees; this is the world in which he grew up and in which until quite recently he lived all his life. But now, at the age of 43, he is finding that world come apart on him. A year ago something unspeakably awful happened: his 12-year-old son, Ethan, off at summer camp, was murdered in a fast- food restaurant, "one of those deaths that make no sense -- the kind where the holdup man has collected his money and is free to go but decides, instead, first to shoot each and every person through the back of the skull." Now he has been left by Sarah, his wife of 20 years, who has been devastated by her son's death and believes that she must start life over because "I don't have enough time left to waste it holing up in my shell," a shell she thinks Macon played a crucial role in constructing.

SO THERE HE IS, alone in the house with Helen, the cat, and Edward, the rowdy little Welsh Corgi to whom he stubbornly clings because the dog was Ethan's. Macon is a creature of firm if peculiar habit who believes that a system can be devised to meet each of life's difficulties; his strategems for breakfast, bedclothes and the laundry are nothing if not ingenious, even if they don't exactly work. Change and disruption frighten him, which makes him perfectly suited to be the author of guidebooks "for people forced to travel on business," accidental tourists who, like Macon, hate travel and much prefer to be at home:

"He covered only the cities in these guides, for people taking business trips flew into cities and out again and didn't see the countryside at all. They didn't see the cities, for that matter. Their concern was how to pretend they had never left home. What hotels in Madrid boasted king-sized Beauty- rest mattresses? What restaurants in Tokyo offered Sweet'n'Low? Did Amsterdam have a McDonald's? Did Mexico City have a Taco Bell? Did any place in Rome serve Chef Boyardee ravioli? Other travelers hoped to discover distinctive local wines; Macon's readers searched for pasteurized and homogenized milk."

It is as Macon heads off on one of his research trips that his life begins to change. The veterinarian who has boarded Edward in the past now refuses to accept him -- "Says here he bit an attendant," the girl tells Macon. "Says, 'Bit Barry in the ankle, do not readmit'" -- so in desperation Macon pulls into the Meow-Bow Animal Hospital. There Edward is cheerfully admitted by "a thin young woman in a ruffled peasant blouse," with "aggressively frizzy black hair that burgeoned to her shoulders like an Arab headdress." Her name is Muriel Pritchett, and when Macon returns to reclaim Edward she tells him that she is a dog trainer on the side, with a specialty in "dogs that bite." As Edward's bad habits become steadily worse, Macon at last turns to her in desperation. It is the beginning of the end of his old world.

He'd been right on the edge. His grief over Ethan's death and the pain caused by Sarah's desertion had just about done him in, just about turned him into "some hopeless wreck of a man wandering drugged on a downtown street." Enter Muriel -- Muriel with her "long, narrow nose, and sallow skin, and two freckled knobs of collarbone that promised an unluxurious body," Muriel babbling away like "a flamenco dancer with galloping consumption," Muriel with her bewildering array of odd jobs and her pathetic young son by a broken marriage and her rundown house on Singleton Street. Love at first sight it is not: "He missed his wife. He missed his son. They were the only people who seemed real to him. There was no point looking for substitutes."

BUT LIFE DEALS things out whether you're looking for them or not. Muriel, a fighter all her days, fights her way into Macon's heart: "Then he knew that what mattered was the pattern of her life; that although he did not love her he loved the surprise of her, and also the surprise of himself when he was with her. In the foreign country that was Singleton Street he was an entirely different person. This person had never been suspected of narrowness, never been accused of chilliness; in fact, was mocked for his soft heart. And was anything but orderly." The accidental tourist has become a traveler -- "Maybe, he thought, travel was not so bad. Maybe he'd got it all wrong" -- whose journeys now are in the heart, whose world has grown larger than he had ever beore imagined possible.

Where those journeys at last lead him is Tyler's secret, though it is no indiscretion to say that in the novel's final pages he faces wrenching, painful choices. But those choices are really less important than the change that has already taken place. Macon Leary has been given the gift of life. A man who had seemed fated to spend the rest of his days in a rut -- "Here he still was! The same as ever! What have I gone and done? he wondered, and he swallowed thickly and looked at his own empty hands" -- has been given new connections, with himself and with others.

This is the central theme of Tyler's fiction: how people affect each other, how the lives of others alter our own. As are her previous novels, The Accidental Tourist is filled with connections and disconnections, with the exaltation and heartbreak that people bring to each other; she knows that though it is true people need each other, it is equally true "that people could, in fact, be used up -- could use eac other up, could be of no further help to each other and maybe even do harm to each other." The novel is filled as well with the knowledge that life leaves no one unscarred, that to live is to accept one's scars and make the best of them -- and to accept as well the scars that other people bear.

And in The Accidental Tourist there are many others: the large and bumptious Leary family, Macon's wonderfully unpredictable boss, the people of Singleton Street, and most certainly Edward, the funniest and most lovable dog within memory. They occupy what indisputably is Tyler's best book, the work of a writer who has reached full maturity and is in unshakable command, who takes the raw material of ordinary life and shapes it into what can only be called art. The magical, slightly fey and otherworldly tone of her previous books is evident here, but more than ever before Tyler has planted her fiction in the hard soil of the world we all know; TheAccidental Tourist cuts so close to the bone that it leaves one aching with pleasure and pain. Words fail me: one cannot reasonably expect fiction to be much better than this.