NO ONE ever said that this American experiment of ours would last forever. Lincoln saw it almost destroyed by a great civil war; Tocqueville held that democracy, demanding of its citizens extraordinary habits of civility and law-abidingness, would be especially vulnerable in foreign conflicts.

Now comes Jean-Francois Revel, by temperament no pessimist, to discern that against a determined, patient, truth-disdaining aggressor, democracies seem driven to conspire in their own defeat. For democratic morality is a morality of peace, civility, and reason; it is ill-equipped to counter sustained and clever barbarism. Their own acquired virtues prevent democratic peoples from diagnosing their foes accurately.

Revel's book has already captured more than 100,000 readers in France; in this country, it is bound to be cited in hundreds of speeches and articles in years to come. A man of neither left nor right, Revel seeks no scapegoats. The fault, he sees, lies in us all.

It would be wrong to confound Revel's argument with James Burnham's, in The Suicide of the West, and with other similar books of a generation ago. Revel is analyzing the new ethos of a new generation, not that of an older generation steeled by the long, dark struggle against a simpler form of barbarism, the Nazis. Communism is far more formidable, deceptive and sinister, while the morality of the West has become more tenderminded. The Dutch lack a moral right to criticize communist repression, runs a recent manifesto (which Revel cites), as long as housing conditions in Amsterdam fail to meet the highest standards of modern comfort . . .!

Nor does Revel quite belong in that traditional circle of doomsayers fr the West: neither with Marx and Spengler, long since discredited, nor quite with Max Weber, Joseph Schumpeter, and Daniel Bell. In material success, such social thinkers have seen decline in virtue and intellect. Revel, by contrast, sees doom precisely in our moral virtues and intellectual habits.

Revel argues, in effect, that we are well prepared to deal with competitors of a certain rationality and civility and perhaps at the limit with adversaries as clearly evil and barbaric as the Nazis. But we cannot deal effectively with adversaries who attack us in the twilight zone, through (distorted) versions of our own ideals of social justice -- adversaries sufficiently duplicitous to mimic the trained strivings of our hearts for peace, negotiations, a relaxation of tensions, and reasoned co-existence. Our habitual framework is that of pluralism and civility. Theirs is the lie. Holding them to be innocent until proven guilty, we must delude ourselves about them.

Thus, instead of diagnosing our adversaries exactly, we blame ourselves for "misunderstanding" them. "Democratic civilization," Revel writes, "is the first in history to blame itself because another power is working to destroy it." We feel guilty for feeling suspicious about our foes; and when we do see them clearly for a moment, we profusely apologize for having done so.

Revel takes up arguments each of us has made, and exposes our self-deceptions one by one. The blunt evidence he amasses is embarrassing.

Revel holds that "people in the West find it hard to bear" the thought of a "merciless struggle" between democracies and communism. That is "the only question that counts" for communist leaders. To democrats, such a view would sin "against tolerance"; in such a game, they can scarcely conceive of the rules. Communism is a sick, sick system, which can maintain itself only by expansion, its sole reason for being, its only talent.

Revel avoids deciding which system is better. He has chosen "uniquely to explore the question of which of the two systems is forcing the other to retreat." What interests him is "the mechanism" in democratic mentality and practice which propels it to slavery and death, at the hands of a system so monumentally incompetent in all things human.

THE book consists of 26 short chapters, organized under four separate themes; it ends with a sober prescription for foreign policy: "Neither War Nor Slavery." Part One describes democracies as a brief accidental appearance in history. When facing external enemies, they habitually awaken with painful slowness and blank incomprehension.

Parts Two and Three lay out the evidence concerning the nature of the empire which now threatens us, which we do not dare to call "evil." People forget that Communism is a western heresy, whose devotees know well, although in a perverse way, the secret springs of our own impulses. Their well-conceived, steadily executed strategy for us, like Salieri'sor Mozart, is to drive us to suicide.

Part Four, "The Mentality of Democratic Defeat," offers a tour of the stages already accomplished, from the moment when cowardice began at the Berlin Wall, through Detente, The Double Standard, and The Comedy of Succession in Moscow. Each chapter stirs anticipatory fear in the pit of the stomach.

As a writer, Revel (like so many French journalist-philosophers) is a master of aphorism. Beautiful little nuggets of clear insight and expression -- the French haiku -- stud the text, interrupt its flow, force the reader to meditate. For my taste, the prose is in this respect a little wearisome. One plods on from the fascination of an advance reading of one's own autopsy.

Still, I find Revel too pessimistic, with respect to the United States at least. During the 1970s, well in advance of their intellectual superiors, ordinary American people did begin to see the long shadow of Soviet power; began to demand greater efforts in self-defense; and then twice elected a president more determined than any since John F. Kennedy to see the Soviets true, and to resist. Inspired in part by religious belief in the justice of opposing the lie by whatever sacrifices are necessary, democracies, it seems, can regain insight into the twilight zone between reason and barbarism, the zone of purposeful deception. Neither nature nor nature's God commands democracies to perish. Moral vigilance of a high order -- and persistence and sacrifice and courage -- are not foreign to democracies. They were not to Lincoln, to Wilson, to Franklin Delano Roosevelt, to Churchill, or to so many others.

We are not as stupid as we often seem, nor as self-deluded, nor as lax in our moral courage. Except . . . Except that democratic leaders, Revel writes, must now make an official visit to Moscow as part of their electoral campaign. The Soviet Union, most often crudely, signals its chosen candidate, often dispatching Gromyko "to add a personal touch." Public opinion, the academy and journalistic elites force democratic leaders into negotiations for their own sake, not to seek advantages for the West but to accommodate. Written in 1982, this book describes several key events in 1984 predictively.

Even President Reagan now seems to believe he can charm the Soviet leaders (if only one of them will live long enough to prepare to sit down with him). He says he will reason with them, to convince them that the democracies mean them no harm. Thus, even President Reagan may now be writing another chapter in how democracies perish.

I want to think Revel too pessimistic. But he has sown a doubt in my mind, and made me want to watch the unfolding evidence with morbid fascination. As Revel writes: "The aim of this book is to describe in detail the implacable democracy-killing machine this world of ours has become. There may be some satisfaction in understanding how it works, even if we are powerless to stop it." Powerless we are not.