OF ALL the catastrophes that have befallen humanity in modern times, what has happened in Cambodia is among the very worst. It is hard to believe that barely more than a decade ago Cambodia was, in most respects, idyllic: primitive yet lush. Phnom Penh was one of Asia's loveliest cities, with the veneer of a French provincial outpost set off against the elegance of Cambodia's natural charms. The countryside was placid; the people seemingly benign.

Today, of course, Cambodia is a wasteland. War, genocide, famine and invasion have descended like the biblical plagues, leaving those who survived to begin again under the hard-eyed rule of Vietnamese occupation. How much the United States is to blame for the Cambodian tragedy can be argued. That we bear some of the guilt is beyond dispute.

It was to underscore what has happened to the Khmer nation -- and the American part in it -- that Jack Anderson says he thought up this project. The Cambodia File is a novel. Anderson supplied, as he puts it, "the raw facts," and his co-author, Bill Pronzini, who has at least 22 other books to his credit, wove the "human saga." The result is a curious collaboration, a mixture of pulp fiction, some graphic, even wrenching, detail and the sort of official documentation (preferably labeled secret) that Anderson has made his stock in trade.

The story covers roughly a year beginning in the winter of 1975 and ending in the spring of 1976, during which Cambodia fell to and was trampled on by the communists. In an unnecessarily self-promotional "Afterword," Anderson takes credit for alerting the world to what was happening in Cambodia during that period, a time when little information was seeping out and only the darkest hints of the torment inside were generally available.

"I tried repeatedly to awaken the world to what was happening behind the sealed Cambodian borders," Anderson asserts, "but my columns were ignored by a world preoccupied with other, more visible, problems."

Rather than let the facts now known speak for themselves, Anderson and Pronzini embellish them with a soap opera-like love story involving a Cambodian woman and an American diplomat, who discovers his conscience only after he has fled Phnom Penh, leaving her to suffer the full ravages of the revolution, until she is able to escape. In addition, there are various other Cambodian and Americans intended to typify good, evil and the various combinations thereof. The characters are wooden. The dialogue is mostly mawkish.

And yet, I can't really say -- as I was tempted to -- that the book is altogether bad, or that it cheapens this horrible chapter in recent world history beyond any justification. The book is redeemed by the sections which portray life under the Khmer Rouge in all its terrible viciousness. (But the full impact of what this bizarre band of Cambodian communists did to their own country is still shrouded in the inaccessibility of the place.)

In the best of times, Americans never knew much about Cambodia. Virtually none of us spoke the language. Few knew the history or understood what is an extraordinarily complex society for all its surface calm. The savagery, therefore, still seems somehow remote. What Pronzini has done is to make the victims and the tormentors more imaginable. The undoing of the human spirit is universally recognizable after all, when it is dramatized in fiction, however conventional it may be.

This passage describes part of the daily regimen in the commune where Than Kim, the Cambodian heroine, is sent after she and the rest of the population of Phnom Penh are driven from the city:

"Kim . . . has grown thin and suffers from back spasms, cramps, and aching joints. Vitamin deficiency. Protein deficiency. Calcium deficiency. They were not permitted any of the first crop of yams and sweet potatoes; these were trucked away to an unknown destination.

"They have never been given meat or fish or prahoc to eat. They are allowed two meals per day, and each consists of a blackish soup which the Khmer Rouge taught them how to make: rice, green bananas, white maize, the water plant traucon , banana stems cut into thin strips. At first the KC laughed and said 'You are pigs; you must be pigs because you eat the food of swine.' Now they no longer laugh. No one laughs in the commune anymore; Kim has not heard the sound of laughter for many weeks."

The more we know about Cambodia, the better we can, in the long run, assess responsibility for what happened there -- indeed, is still happening there. (What may well be the best account is being written now by Dith Pran, a young Cambodian journalist who survived four years of the Khmer Rouge regime and escaped with his remarkable sensitivities intact. His co-author is Sidney Schanberg of The New York Times who worked with Pran in Cambodia.)

In a sense, this book represents the good and bad sides of Jack Anderson. He plays a unique role in American journalism, tackling sensitive subjects head on with a permanent sense of indignation at wrongdoing and a determination to get the news that officials must prefer to keep quiet. But Anderson diminishes his own admirable work by his breathless, often simplistic presentation. In reducing things to the quick takes of his columns and broadcasts, Anderson frequently creates a caricature of what he means to say.

And so it is with The Cambodia File . The point is to make us aware of ghastly truths and on that score, the book serves its purpose. But the manner of presentation is cruder, emptier than the tragic subject deserves.