In the last chapter of his marvelous 1987 book “The Counterlife,” Philip Roth sends his alter ego Nathan Zuckerman to the heartland of “Christendom,” provincial England. Sitting in a restaurant with his English wife, Zuckerman hears another patron, a “large, white-haired, elderly woman,” loudly command a waiter: “You must open a window immediately – there’s a terrible smell in here.” Immediately, Zuckerman is convinced that the old woman is an anti-Semite, and that her nasty comment is meant for his ears. His wife pleadingly suggests that the old woman might be complaining about someone wearing too much perfume, or that she is simply drunk; but Zuckerman is not to be dissuaded. “I am that stink,” he grimly insists.

Seventeen years later, the shock of this moment returns, in a still uglier form, in Mr. Roth’s new novel, “The Plot Against America” (Houghton Mifflin, 391 pages, $26). It is the early 1940s, and 7-year-old Philip Roth is on a trip to the nation’s capital; after a day of sightseeing, his family goes to a cafeteria for dinner. But when his father, Herman, launches into a monologue in praise of Walter Winchell, another diner comes up to their table and denounces Winchell, and by implication Herman himself, as “a loudmouth Jew.” The cafeteria owner apologizes effusively, and Herman insists that the family stay and finish their meal. But the stink of anti-Semitism, once in the air, cannot be ignored. Washington D.C., the capital of a nation devoted to freedom and equality, has been turned by one anti-Semitic crack into just another outpost of “Christendom” – another place where Jews do not belong.

In “The Counterlife,” however – as in all of his best books, from “Goodbye, Columbus” to “Portnoy’s Complaint” to “The Ghost Writer” – Mr. Roth refuses to allow this Jewish vulnerability to determine the shape and language of the novel itself. Indeed, no writer has done more than Mr. Roth to satirize the anxiety of Jews confronted with anti-Semitism, the totalizing logic that sees in an idle insult the prelude to pogroms and concentration camps. Everything that makes Mr. Roth a great novelist – his rage, his subversive comedy, and his slipperiness – is a protest against that fear, and against the values it breeds: caution, diplomacy, anxious respectability.

That is why Mr. Roth’s early fiction, which the official voices of American Judaism so violently denounced, is actually an unmistakable tribute to the success of American Jews. America, Mr. Roth’s comedy assumes and declares, is the one place where Jews do not have to be cautious, diplomatic, and respectable. America’s safety licenses Mr. Roth’s danger: the first chapter of his memoir, “The Facts,” is titled “Safe at Home.” That security was the legacy of the Newark childhood Mr. Roth has alternately mocked and celebrated in his writing: “The only nation for Jews, as I saw it,” he writes in “The Facts,” “was the democracy to which I was so loyally – and lyrically – bound.”

Yet while this security is what makes Mr. Roth’s fiction possible, he is too much of a novelist – and, he might say, too much of a Jew – simply to take it for granted. In the same memoir where he declares himself “safe at home,” Mr. Roth remembers the near-riot that ensued when his Jewish high school’s football team defeated their Christian rivals, and a rampaging mob invaded “the sacred heart of my inviolate home land.” It is those moments of betrayal, when the seemingly inviolate is violated, that strike rage and terror into Nathan Zuckerman and Herman Roth. For they seem to prove that the whisper of Jewish fear was right after all, that there is no place the Jews can feel at home, not even in America.

“The Plot Against America” is a startling book because it shows Mr. Roth appearing to agree, for the first time in his career, with all those inner and outer voices of caution. Mr. Roth, who has mastered so many permutations of outrage, tops himself with the outrageous suggestion that it is not safe for a Jewish writer to be outrageous in America – or at least not in the counter historical America of “Plot,” which resembles the world of Mr. Roth’s memoir in every detail. Again we are in the Weequahic section of Newark in the 1940s, again we find the insurance-salesman father, the devoted mother, the gangsters and shopkeepers and ballplayers – with one glaring exception: In this version, the President is not Franklin D. Roosevelt but the isolationist, Jew-baiting, indefeasibly heroic Charles Lindbergh.

The plot of “Plot” has been discussed so widely that this Twilight Zone twist will no longer come as a surprise to most readers. This is no great loss, however, since the alternative history Mr. Roth proposes is the least successful of the book’s inventions: Almost no historical imagination has been devoted to making the Lindbergh presidency plausible. Mr. Roth has Lindbergh defeating Roosevelt in a landslide in the 1940 election, running on a platform of peace at any price. The reasons why this did not happen, and could not have happened – political, sociological, economic – do not interest Mr. Roth; Lindbergh’s election is the novel’s donnee, and the reader must simply accept it as such. So, too, with the still more incredible conclusion, in which the course of history as we know it is resumed without the slightest alteration – Roosevelt is returned to office, Pearl Harbor is bombed (in 1942 instead of 1941), and America wins the war.

It would be a mistake, however, to complain too much about this seeming abdication of imagination. By making the Lindbergh presidency a strictly self-contained, two-year-long episode, without plausible cause or consequence, Mr. Roth leaves no doubt that what he is writing is not counter history or science fiction, but a thought experiment. More precisely, “The Plot Against America” is an experiment in self-torture, the product of an obsessively indulged and elaborated neurosis. And the neurosis, as always in Mr. Roth’s work, is Jewish fear. What Mr. Roth has done is to take the worst fears aroused by a situation like the restaurant episode in “The Counterlife” and give them free rein; instead of a passing insult, the cafeteria episode in “Plot” is the first in a steadily ascending series of traumas, which culminates in pogroms and mass murder.

This is not to suggest that “The Plot,” because it is a book about a neurosis, is a neurotic book. On the contrary, Mr. Roth’s imagination of Lindbergh’s America evidences a nearly diabolical ingenuity and control. If fascism had come to America, it would surely have been just like this. Instead of bullying Gestapo thugs, there would be smiling FBI agents, like the one who tells the young Philip to trust him because he’s just like the G-men heroes of “Gangbusters.” Instead of concentration camps, there would be “Homestead 42,” a “voluntary” relocation program in which the government orders corporations to reassign their Jewish employees to Kentucky or Montana. Instead of Julius Streicher, there would be Rabbi Lionel Bengelsdorf, the head of Lindbergh’s “Office of American Absorption,” who serenely tells America’s Jews to be thankful for this opportunity to “enter as far into the national life as they like.” Above all, one feels, this is what fascism would feel like to a 7-year-old boy: a matter not of public evil but of family quarrels, inexplicable rages and anxieties, sudden dislocations.

But while Mr. Roth’s inventions are ineluctably gripping – as gripping as fear itself – the time comes when the reader shakes himself awake and begins to question them. Since it didn’t happen here – and since Mr. Roth’s own career is one of the best proofs that it didn’t – why has the story of “The Plot Against America” seized its author’s imagination only now, after 50 years of writing? And why has it so obviously seized the imagination of critics – so much so that one, Ron Rosenbaum, reviewed the book some four months before publication?

The answer is not far to seek: It is September 11, and everything that has happened since, that gave Mr. Roth his renewed imagination of vulnerability. “The Plot Against America” is a manifestation of the same anxiety that has appeared in every corner of Jewish American life in the last few years. It can be seen in the political delusions of Art Spiegelman’s “In the Shadow of No Towers”; in Woody Allen’s film “Anything Else,” which features Allen as a comically paranoid, gun-toting survivalist; in New York magazine, where a cover story on Jewish fear quoted Nat Hentoff declaring that he would not be surprised to see Jews assembled for deportation in Times Square; in Mr. Rosenbaum’s New York Observer column on the imminence of a second Holocaust in Israel (a fear expressed by Mr. Roth in his 1993 novel “Operation Shylock”).

As this list shows, fear does not encourage a writer’s best work or sanest thought. “The Plot Against America” is no exception: Its prose is some of the worst Mr. Roth has written, bureaucratic and unobservant, full of run-on sentences staggering under the load of information. (“On June 22, 1941, the Hitler-Stalin Non-Aggression Pact – signed two years earlier by the two dictators only days before invading and dividing up Poland – was broken without warning when Hitler, having already overrun continental Europe, dared to undertake the conquest of the enormous land mass that stretched from Poland across Asia to the Pacific by staging a massive assault to the East against Stalin’s troops.”)

More troubling, however, is the way Mr. Roth, like so many others, has transformed our present anxiety about Islamic terrorism into a more conventional, and thus less threatening, anxiety about right-wing oppression. Today, the plot against America, and against Jews, is not being hatched in Berlin or Montana but in Iraq and Afghanistan. If Mr. Roth’s novel, by exorcising our irrational fears, allows us to better confront our rational ones, it will have performed a valuable service.